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Design by JOHN CLARKE Speech Timer For Contests & Debates If you are involved in school or university debating contests or in Toastmasters International, you will be aware of the importance of a speech timer. It keeps meetings and events on time and also prevents individual speakers from droning on past their allotted time. The timer presented here has a large 3-digit display plus three large LEDs and a buzzer. Plus, it has a tiny infrared remote control. T HE INITIAL impetus for this Speech Timer project came from a member of Toastmasters International who was concerned at the primitive timer employed at his club. Could we design a timer which met Toastmasters International rules but did not involve an olde-worlde mechanical timer and three crudely switched coloured lights? Well, of course we could! Mind 68  Silicon Chip you, Toastmasters rules do not make any mention of 3-digit LED 7-segment displays – those rules were drawn up over 80 years ago when carbon-zinc batteries and incandescent lamps were state-of-the-art technology! Microcontrollers, light emitting diodes and infrared remote controls would have been unimaginable! So our Speech Timer provides the basic green, amber and red warning lights plus a manually-operated final alarm, as required for speeches defined by Toastmasters’ rules. It also provides a 3-digit up/down timer, all controlled by a cheap microcontroller. Specifically, we have incorporated preset time periods that match Toastmasters International rules for various speech lengths. Table 1 shows the details. These time periods are based on the siliconchip.com.au Clock Brightness Features & Specifications A B Presets Up or Seconds < Reset Pause Presets Down or Seconds Specifications •  Power: 12V DC <at> 100mA •  Current drain: 76mA typical at full brightness; up to 100mA with warning •  •  •  •  LED and Alarm on Audible alarm: 1.22kHz tone modulated at 200Hz Display multiplexing: 100Hz Low battery indication: warning turns on below 8.8V and off above 8.92V (voltage sampled at 3.3-second intervals) Latency: ~18ms from press of IR remote button to timer response July 2015 to June 2016 Speech Contest Rule Book. By the way, there are apps and software to time speeches at Toastmasters’ meetings but these are not really useful when they must be seen by a room (or even a hall) full of people. Naturally, the Speech Timer can also be used to time speakers in debating contests and meetings. In fact, it can be used anywhere a highly-visible digital timer is required. By default, it counts up but it can also be made to count down (see panel later in the article). Presentation The SILICON CHIP Speech Timer is housed in plastic case with the 3-digit 7-segment LED display on the front. Down the righthand side are the three large LEDs, arranged like traffic lights with red at the top, amber in the middle and green at the bottom of the stack. These are duplicated on siliconchip.com.au C Remote Control in the September 2015 issue. This remote measures just 80 x 40 x 7mm and is powered by a CR2025 3V cell. It has nine pushbuttons or more correctly, small snap-action domes. The buttons are Power Start (shown as a circle logo with a stroke through the top), A, B and C and a 5-button array. We have assigned the buttons as shown in Fig.1. The power button is used for controlling the display brightness while buttons A, B and C are the warning indication controls: A for manually sound the Alarm, B for the warning LED Brightness and C for manually Cycling through the warning LEDs. The functions of the 5-button array are described later in this article. A tiny blue LED on the Speech Timer’s front panel flashes to acknowledge signals from the infrared remote control and it doubles as a low-battery indicator, staying lit when the battery voltage is low. Cycle Alarm/ Warning Volume Brightness Warning Colours > •  •  •  •  •  •  •  •  •  •  •  •  •  •  •  •  Battery and/or DC plugpack operation Readout on large 7-segment displays Visual warnings via green, amber and red indicator lights Audible warning buzzer (manually-operated) Optional automatic visual warning operation Manual visual and buzzer warning control Separate duplicated warning lights for timekeeper and speaker Dimming of main display and warning lights Volume adjustment for audible warning signal 99-minute maximum time period Preset Toastmasters’ contests and other presets included Minutes and tens-of-seconds display (seconds display accessible) Infrared remote control operation Reset, pause and start timer controls Blue acknowledge LED for IR signalling Low battery indicator < Features Fig.1: this artwork is attached to the top of the case and shows the button assignments on the remote control. the rear of the case, together with the small loudspeaker which provides the ending buzzer. The Speech Timer can be placed in the room so that the audience and the speech timer can see the 3-digit display, while the speaker can only see the green/amber/red LEDs when they are lit. The Speech Timer can be run from an internal battery (eight AA alkaline cells) or from a 12V DC plugpack. You can also use NiMH or Nicad cells instead of alkalines and these can be trickle charged via the 12V plugpack. Remote control Apart from an on/off switch mounted near the socket for the DC plugpack, there are no controls on the unit. Instead, all functions are set by a tiny remote control, made by SparkFun – the same unit as used in our 9-Channel > Circuit description Fig.2 shows the complete circuit of the Speech Timer. It’s based on a PIC16F88 microcontroller (IC1) and this drives the 3-digit 7-segment LED display and warning LEDs (via transistors Q1-Q8 and IC2 & IC3). IC1 also monitors the output from the infrared receiver (IRD1) and the supply voltage. Each of the LED display segments comprises four series-connected LEDs evenly spaced apart and there are two series-connected LEDs for the decimal point. When a segment is lit, it will typically have 7-8V across the four series-connected LEDs. That presents a design problem since IC1 requires a 5V supply while the displays need to be driven from a supply voltage of 12V. We solved that conundrum by tying IC1’s positive (Vdd) supply rail to the +12V supply rail, while its negative rail is supplied from a 7905 3-terminal regulator. The segment anode lines of the 3-digit display are driven by PNP transistors Q1-Q8 (for the seven segments plus the decimal points). The emitter of each transistor is connected to the December 2015  69 Table 1: Preset & Manual Time Periods (Counting Up) Type Length (minutes) (Display when unit reset) Green Warning Amber Warning (elapsed (minutes or minutes) minutes:seconds) Red warning (elapsed minutes) Disqualification Minimum Period (minutes:seconds) Disqualification Maximum Period (minutes:seconds) Any (manually operated) Table Topics* 0:0 when selected when selected when selected 1-2 1 1:30 2 1:00 2:30 Evaluation* 2-3 2 2:30 3 1:30 3:30 Tall Tales* International & Humorous* Speech1 3-5 3 4 5 2:30 5:30 5-7 5 6 7 4:30 7:30 10' 7 9 10 Speech2 15' 10 13 15 Speech3 20' 15 18 20 Speech4 30' 20 25 30 Speech5 40' 30 35 40 Speech6 50' 40 45 50 Speech7 60' 50 55 60 Speech8 70' 60 65 70 Speech9 80' 70 75 80 Speech10 90' 80 85 90 +12V supply and the collector connected to the segment anode via an 82Ω current-limiting resistor or via a 180Ω resistor for the DP (decimal point). Each segment line is driven when the base of its transistor is pulled low by the respective output of IC1. When the base is taken high (ie, +12V), the transistor is switched off and the segments are off. As shown on the circuit, outputs RA3, RA4, RB1, RB2, RB4, RA0, RB7 & RA2 of IC1 connect to the bases of transistors Q1-Q8 via 470Ω resistors. The three common cathode 7-segment displays are multiplexed. This means that the seven anode segments and the decimal points of the digits are driven by the eight transistors and then each digit is turned on for about one-third of the time by pulling its common cathode low. For a digit to light, its common cathode needs to be connected to the 0V line of the 12V supply. But we can’t directly do this via any of IC1’s outputs since IC1’s negative rail (GND) is only 5V below the +12V supply rail. So the circuit needs level shifting from the negative rail of IC1 to 0V. IC2 & IC3 take care of this level shifting requirement and drive the common-cathode connections at the same time. IC2 is a 4051 analog single-pole 8-way switch that’s used as a single pole 4-way switch. IC2 can 70  Silicon Chip connect its common pole contact “Z” at pin 3 to one of the Y0, Y1, Y2 & Y3 terminals. Which connection is made depends on the logic level at the A0 and A1 inputs and that is under the control of IC1. IC2 has separate supply rails for the control inputs (Vss) and for its output switching (Vee). Vss, pin 8, is connected to ground, the negative supply line for IC1, while Vee is tied to the 0V rail. So IC2 does the signal level shifting. The A0 and A1 inputs of IC2 are driven from the RB6 and RB5 outputs of IC1 respectively. When both inputs are low, the Y0 output of IC2 connects to the Z pole contact of IC2 and is pulled high via a 4.7kΩ resistor. This output then drives the 4B input of IC3. IC3 is a ULN2003 7-Darlington transistor open-collector driver. We use four of these Darlingtons to separately drive the common cathodes of the 7-segment displays and the common cathodes of “traffic light” LEDs 1-6 and the acknowledge/low battery indicator LED (LED7). When 4B is driven, the 4C collector (pin 13) connects the common of display DISP1 to 0V, so that digit lights up. Other combinations of the A1 and A2 inputs select the Darlington transistors at IN5, IN2 and IN3. For example, when A1 and A2 are both high, IC2’s Y3 output drives 5B of IC3. IC3’s 5C collector then connects the common * Denotes Toastmasters contests. ' is the symbol for minutes of DISP2 to 0V and the second digit lights up, and so on. We drive DISP1 for 2.5ms, then DISP2, DISP3 and then the LEDs, all for the same 2.5ms period. Flashing colon display Note that the connections to DISP3 are mixed up compared to the connections to DISP1 & DISP2. For example, the “A” segment for DISP1 is connected to the “A” segment of DISP2, but this connects to the “F” segment of DISP3. The reason for that is partly due to the fact that DISP3 is actually mounted upside down compared to the others, so that we can have a flashing colon between DISP2 & DISP3. Also, the connections to DISP3 have been done in this way to make the PCB pattern practical. Which segments are driven for each display is sorted out in the software for IC1, so the different connections for DISP3 do not matter. Several different resistor values are used for driving the displays and LEDs. We use 82Ω for the segments but the decimal points for DISP1-DISP3 use a 180Ω resistor. This is because the decimal points have only two LEDs, compared to four in the segments. A similar comment applies to the indicator LEDs, where the resistor values are selected to produce a similar brightness to the 7-segment displays. For the red and amber LEDs, 330Ω siliconchip.com.au siliconchip.com.au December 2015  71 + – B B 33pF 0V 4.7k C E E Q9 BC327 RB0 Vdd RA5/MCLR 14 RB1 RA4 16 15 9 RB5 RB6 RA2 TO SPEAKER 5 Vss CON2 OSC1 OSC2 PWM/RB3 RB7 RA0 11 12 1 13 17 8 7 3 2 100nF RA3 +12V K D1 1N5819 A RB2 IC1 PIC1 6F8 8 PIC16F88 18 10 RB4 AN1 –I/P 6 470 µF 33pF Q10 BC337 C 100nF 2.2k X1 20MHz BATTERY VOLTS DETECT 1 4 4.7k 8 x AA CELLS K SPEECH TIMER 2 λ 3 100Ω 10 µF CON1 A D2 1N5819 3 6 9 10 11 8x 470Ω 1W 15Ω 4.7k B Q5 B Q3 B Q1 EN 1 5 2 4 8 Vss Vee 7 Y0 Y1 Y2 13 14 15 IC2 40 51 B Y3 12 Y4 Y6 Y7 10 µF A1 16 Vdd B Y5 A2 C C C E Q7 C E E E B Q6 B Q4 B Q2 C C C 10 µF B E Q8 C E E E 8 x BC327 A0 Z POWER FOR NiMH & Nicad CELLS ONLY – SEE TEXT S1 7 7B 6 6B 5 5B 4 4B 3 3B 2 2B 1 1B E 8 OUT GND dp fe g d e b c a f 7C 10 6C 11 5C 12 4C 13 3C 14 2C 15 1C 16 9 7 6 4 3 2 9 10 8 DISP1 K 1 d g a K 5 dp c b f 0V +12V dp fe g d e b c a K 1 d g a K 5 DISP2 MINUTES +12V TP GND 7 6 4 3 2 9 10 8 10 µF TENS OF MINUTES REG1 7905 COM IC3 ULN2003 180Ω 82Ω 82Ω 82Ω 82Ω 82Ω 82Ω 82Ω 0V IN 10 µF dp c b TP +12V 9 10 2 7 6 3 4 8 c dp b db c e a f dp g K 1 E a g K 5 f e 6 b 9 f 10 g 2 e 1 B C BC 32 7 , BC337 d DISP3 K TENS OF SECONDS A 1N5819 2 3 IRD1 K A 34 5 8 12 λ LED7 λ LED6 λ LED3 λ LED5 λ LED2 K K K K K λK K LED4 K IN 76 ACK/LO BAT. A A A A A λ LED1 AA A LEDS OUT 10 470Ω 1k 1k 330Ω 330Ω 330Ω 330Ω IN GND 7 9 05 Fig.2: the Speech Timer circuit is based on a PIC16F88 microcontroller (IC1). This drives a 3-digit 7-segment LED display, six warning LEDs (LEDs1-6) and a blue acknowledge LED (LED7) via transistors Q1-Q8 and IC2 & IC3. IC1 also monitors the output from the infrared receiver (IRD1) and the supply voltage. SC 20 1 5 IRD1 12V DC IN (IRD1 – UNDER) 19111151 100Ω 470Ω LAY ON (LED7 UNDER) SIDE + 10 µF A A Q2 Q4 Q5 470Ω Q3 470Ω 470Ω 470Ω 82Ω + 82Ω 82Ω 82Ω 82Ω 1k + 470Ω 100nF X1 20MHz TP + +12V + 10 µF TP 100nF GND BC327 Q9 10 µF IC3 ULN2003 Q6 470Ω 1k 4.7k IC2 4051B Q7 GREEN LED6 S1 2.2k 4.7k 470Ω 3x BC327 Q8 IC1 PIC16F88 Q1 5x BC327 4.7k 33pF A AMBER LED5 470Ω 33pF 82Ω 82Ω 180Ω 330Ω 330Ω 330Ω 330Ω RED LED4 TP 0V BC337 Q10 Q1-Q9 = BC327 Q10 = BC337 + CON2 REG1 7905 5819 – D2 TO SPEAKER 470 µF + 12V D1 5819 CON1 15 Ω 1W FOR NiMH & NiCd CELLS ONLY – SEE TEXT 10 µF 10 µF LOOP TO BATTERY HOLDER Fig.3: follow this diagram to install the parts on the rear of the PCB. Note that PC stakes are installed at the three test points (TP) and at the LED4-LED6 positions. LEDs4-6 are then mounted proud of the PCB, as described in the text. resistors are used. The green LEDs are much brighter for the same current and so the current in these is further reduced using 1kΩ resistors. A 470Ω current limiting resistor is used for blue LED7. Dimming is achieved by switching the displays off for part of the normal 2.5ms on period. Infrared receiver Infrared receiver IRD1 receives the signal sent by the SparkFun remote. A unique code is transmitted from the remote for each separate pushbutton and the infrared signal is sent as 38kHz This oscilloscope grab shows the modulated 1.22kHz signal across the loudspeaker when the alarm is sounding at full volume. 72  Silicon Chip bursts, using coding that is known as Pulse Distance Protocol. For further information about the infrared coding, refer to the 9-Channel Infrared Remote Control article in the September 2015 issue – see www.siliconchip.com.au/ Issue/2015/September IRD1 includes an amplifier and a demodulator. Demodulation removes the 38kHz component and IRD1’s pin 1 output goes low when it is receiving the pulsed 38kHz signal and high in the absence of signal. IC1 decodes the incoming signal from IRD1 and reacts to any valid coded signal. So, for example, when the “A” button is pressed on the remote control, the speaker will be driven. This alarm signal comprises a 1.22kHz signal modulated at 200Hz. This 1.22kHz signal is produced by a PWM (pulse width modulated) output at pin 9 of IC1. The signal is buffered using complementary transistors Q9 & Q10 and AC-coupled to the loudspeaker via a 470µF capacitor. The volume is set by the actual pulse width of the signal, with a 50% duty cycle giving maximum volume. The accompanying scope waveform shows the signal across the loud- speaker when sounding an alarm at maximum volume. The alarm signal comprises six or seven cycles of the 1.22kHz tone modulated on and off at a 5ms rate. Clock signal IC1 runs at 20MHz using crystal X1, to ensure timekeeping accuracy. 20MHz is used in preference to a lower frequency such as 4MHz, as the software requires considerable processing to drive the displays, update the timer and decode the infrared signal without faltering. The battery voltage is monitored at analog input AN1 (pin 18) of IC1, via a 2.2kΩ and 4.7kΩ resistive divider. IC1 converts the monitored battery voltage to a digital value and compares this against the low-battery voltage threshold of 8.8V. If the battery voltage is low, it turns on LED7 continuously, at a low level. LED7 also flashes when IC1 receives a valid signal from the remote control. As previously noted, the circuit can be run from a 12V DC plugpack and/ or a battery comprising eight AA cells. They are connected to power switch S1 via Schottky diodes D1 & D2. These siliconchip.com.au This view shows the fully-assembled PCB. The 15Ω 1W resistor at bottom left is installed only if rechargeable NiMH or Nicad cells are fitted to the unit. Be sure to leave this resistor out if you intend using alkaline cells. diodes provide reverse polarity protection and isolate the 12V plugpack supply from the AA cells. D2 could be a standard 1N4004 instead but a Schottky diode is specified to avoid any mix up when installing D1 & D2. A 15Ω 1W resistor can be fitted between the battery and the 12V supply following D2 to allow trickle charging of rechargeable NiMH or Nicad cells. This resistor must be omitted if alkaline cells are used. REG1 is a 7905 negative regulator which provides the 5V supply to IC1. As shown, 10µF supply decoupling capacitors are included at the input and output of this regulator while the supply to IC1 (pin 14) is further decoupled with a 100nF capacitor. mounted on both sides of the PCB. Most of the parts are mounted on the “rear” of the PCB, while the “front” carries the three 7-segment LED displays (DISP1-DISP3) plus five other parts, including the infrared receiver (IRD1). Begin the Speech Timer assembly by installing the parts on the rear of the PCB – see Fig.3. The resistors can go in first, taking care to ensure that the correct value goes in each location. Table 2 shows the resistor colour codes but you should also check each one using a digital multimeter (DMM) before soldering it into position. Note that the 15Ω 1W resistor is Building it Building the Speech Timer is easy since all the parts are mounted on a double-sided PCB coded 19111151 (162.5 x 102mm). This is housed in a UB2 plastic case (197 x 113 x 63mm), with the lid replaced by a red Perspex or acrylic transparent sheet. Alternatively, a cut-out can be made in the lid that comes with the case and a transparent window fitted to this cut-out. As shown on Figs.3 & 4, parts are Table 2: Resistor Colour Codes   o o o o o o o o o o siliconchip.com.au No.   3   1   2   9   4   1   1   7   1 Value 4.7kΩ 2.2kΩ 1kΩ 470Ω 330Ω 180Ω 100Ω 82Ω 15Ω 4-Band Code (1%) yellow violet red brown red red red brown brown black red brown yellow violet brown brown orange orange brown brown brown grey brown brown brown black brown brown grey red black brown brown green black brown 5-Band Code (1%) yellow violet black brown brown red red black brown brown brown black black brown brown yellow violet black black brown orange orange black black brown brown grey black black brown brown black black black brown grey red black gold brown brown green black gold brown December 2015  73 15111191 C 2015 19111151 rev.1 MINUTES x10 DISP1 DISP2 f b DISP3 dP b e c dP 1 2 3 4 5 1 2 3 4 5 A d c b AMBER LED2 f A dP RED LED1 e g c d 5 4 3 2 1 A g g NB: DISP3 MOUNTS UPSIDE DOWN SECONDS x10 a f d A LED7 10 9 8 7 6 a e LOW BATT. IRD1 MINUTES 10 9 8 7 6 8 88 SPEECH TIMER a GREEN LED3 6 7 8 9 10 Fig.4: here’s how to install the parts on the front of the PCB. The 7-segment LED displays (DISP1-DISP3) plug into 5-way SIL socket strips and DISP3 must be installed upside down. IRD1, LEDs1-3 & LED7 are all mounted proud of the PCB, as described in the text (see also Figs.5 & 6). only installed if you intend to run the Speech Timer using NiMH or Nicad cells. DO NOT install this resistor if you will be using alkaline cells. Diodes D1 & D2 can go in next, followed by an 18-pin DIL socket for IC1. Make sure that these parts are all orientated correctly before soldering them to the PCB. IC2 & IC3 can then be fitted and these parts can either be directly soldered in place or mounted via 16-pin sockets. Regulator REG1 is next on the list. As shown, this part mounts horizontally with its leads bent down through 90° to fit into the allocated holes. Fasten the regulator’s tab to the PCB using an M3 x 6mm screw and nut before soldering its leads. Don’t solder the leads first – you could crack the PCB Make sure that all the pins on the 7-segment LED displays go into the SIL sockets when they are installed. 74  Silicon Chip tracks or pads as the tab is fastened down if you do. Crystal X1 can now be fitted; it’s mounted just to the right of IC1 and can go in either way around. That done, install PC stakes at the 12V supply positions near CON1 (to connect the battery leads), at the TP 12V, TP GND and TP 0V positions and at the LED4-LED6 positions. The next step is to mount transistors Q1-Q10. Note that Q1-Q9 are all BC327s, while Q10 is a BC337. Make sure that the BC337 goes in the Q10 location. Make sure also that the tops of the transistors sit no more than 10mm above the PCB, otherwise they will later foul the AA cells (if fitted). Now for the capacitors. Install these as shown, making sure that the electrolytic types are correctly orientated. Note that the 10µF electrolytic capacitor at top left must be installed with its side flat against the PCB (see photo), so that it will later clear the AA cells. Follow with the DC socket (CON1), the screw terminal block (CON2) and switch S1. Be sure to install CON2 with its wire entry side towards REG1. That completes the assembly on the rear side of the PCB apart from siliconchip.com.au Take care to ensure that the LEDs and the three 7-segment displays are all orientated correctly. Note that DISP3 is installed upside down in order to obtain a flashing colon. The diode test facility on a DMM can be used to sort out the LED colours (see text). LEDs4-6. Leave these off for the time being. Front PCB assembly Fig.4 shows the layout on the front of the PCB. The first step is to install six 5-way SIL (single in-line) socket strips to mount the three 7-segment displays. These socket strips are cut from three 14-pin IC sockets and the cut edges filed to a smooth finish before installation. Be sure to push the socket strips all the way down so that they sit flush against the PCB before soldering their pins. Next, cut the pins on each 7-segment display to 4mm in length using a pair of side-cutters. That’s best done by first cutting a 4mm-wide length of cardboard and then holding this against the pins as they are trimmed. Don’t install the displays just yet though. That’s done after the remaining parts have been installed on this side of the PCB. LEDs1-3 can go in first. These must all be orientated correctly, with the longer anode leads going to the “A” position, and they must be mounted on 12mm lead lengths. These LEDs all come with clear lenses, so you will have to sort out which siliconchip.com.au is red, which is amber and which is green. That’s easily done by using the diode test facility on a DMM. Each LED should light when the DMM’s probes are connected with the correct polarity (ie, red to anode, black to cathode). Use a 12mm-wide cardboard spacer to set the LED heights. It’s just a matter of sliding the spacer between the leads, pushing the LED down onto the spacer and then lightly tack soldering one of the leads. The other lead can then be soldered, after which extra solder can be added to the first lead. Once all the LEDs are in place, tin their leads from the PCB to just shy of the plastic lenses. This will stiffen the leads and ensure that the LEDs cannot be pushed in from the front panel when the PCB is installed in the case. Alternatively, before installing the LEDs, fit their leads with 12mm lengths LED7 DETAILS 13mm A PCB K Fig.5: LED7 is stood off the PCB on 13mm long leads, as shown here. of 1mm-diameter heatshrink sleeving (this will also eliminate the need to cut a cardboard spacer). LED7 is fitted in similar fashion on 13mm-long lead lengths (Fig.5). Once again, its anode lead is the longer of the two and there’s a flat side on the plastic body adjacent to the cathode. Now for the infrared receiver. Fig.6 shows how this part is mounted. First, bend its leads down through 90° exactly 5mm from its body, then fit it to the PCB on 15mm vertical lead lengths (use a 15mm-wide cardboard spacer to set this). It’s a good idea to lightly tack solder one lead first, then check that all is correct before soldering the remaining two pins and then refreshing the first pin with extra solder. Installing LEDs4-6 The PCB can now be flipped over IRD1 5mm 15mm Fig.6: the mounting details for IRD1. Its body sits 15mm above the PCB. PCB December 2015  75 all been correctly trimmed to 4mm, as described earlier. Battery holder connections This view shows the case lid with the red Perspex window in place and the holes drilled and cut for the LEDs & IRD1. and LEDs4-6 installed. These LEDs must be installed so that their plastic bodies are 34mm above the PCB and to do that, it’s necessary to solder their leads to tinned copper wire risers. The first step is to fit 35mm lengths of 1mm-diameter tinned copper wire to the six PC stakes in the LED locations. Make sure that these wires are perfectly straight and vertical. You can straighten tinned copper wire by clamping one end in a vice and then stretching it slightly by pulling on the other end with pliers. Once the risers are in place, cut a 34mm-wide cardboard strip and use this as a guide to trim the wire lengths so that their ends are exactly 34mm above the PCB. The next step is to cut six 25mmlengths of 2mm-diameter heatshrink sleeving. These are then slipped over the risers and the PC stakes, leaving bared 9mm-long wire ends at the top. The final step is to install the LEDs. As before, you will first have to use The PCB is secured to the case lid on four M3 x 15mm tapped Nylon spacers. 76  Silicon Chip the diode test facility on a DMM to sort out the colours. That done, install LED4 by first feeding its leads down the heatshrink tubing. Push it all the way down until its body contacts the tops of the risers, then solder each lead to its riser between the heatshrink and the LED’s body. Repeat this procedure for LEDs5 & 6, taking care to ensure that the LEDs are correctly orientated. Finally, complete the PCB assembly by plugging in the three 7-segment displays (DISP1-DISP3). There’s just one thing to watch out for here: DISP3 must be fitted upside down, so that its decimal point is at top left (see Fig.4). As explained earlier, that’s done to obtain a flashing colon between DISP2 and DISP3. Note that the top surfaces of the displays should be 15mm above the PCB when they are installed. Check that this is so and if not, check that the 5-way SIL socket strips have been installed and that the display leads have As shown on Fig.3, the leads from the battery holder are looped through two stress relief holes in the PCB. They are then soldered to the supply PC stakes, with the red wire going to the positive terminal and the black wire to the negative terminal. If you are using two 4-AA holders instead of a single 8-AA holder, it will be necessary to connect the two holders in series. That’s done by connecting the red wire from one holder to the black wire from the second holder. The easiest way to do that is to feed these red and black wires through the two stress relief holes and connect them to the two terminals marked LOOP on the PCB. The remaining red and black wires are then also fed through the stress relief holes and connected to the 12V PC stakes as before (enlarge the stress relief holes if necessary). Case preparation The PCB assembly can now be put aside while you drill and cut the necessary holes in the case. As mentioned previously, the lid can be replaced with either a Perspex or acrylic transparent red sheet (195 x 110mm). Alternatively, you can use the lid supplied with the box and make a cut-out (fitted with a transparent window) for the 7-segment display. The first step is to download the drilling template file (in PDF format) from the SILICON CHIP website (go to www.siliconchip.com.au and search for the project). Print this template out, then cut out the individual sections and attach them to the case using adhesive tape. If you are completely replacing the lid, then you don’t have to make the rectangular cut-outs for the displays or for infrared receiver IRD1, since they simply sit behind the transparent panel. However, 3mm holes will be required for the four corner mounting positions where it attaches to the box pillars (see the template). Conversely, if you are using the lid, you will need to make the rectangular cut-outs. In either case, it’s best to use a pilot drill (eg, 1mm) to start the holes and then enlarge them to size. All the small holes are 3mm diameter, while the larger holes are 10mm diameter. siliconchip.com.au The larger holes should be drilled out to about 4mm and then carefully reamed to the correct size. It’s best to ream one of these larger holes first, so that one of the 10mm LEDs just fits. You then push the reamer into the hole as far as it will go and wind a ring of tape around the shaft (on the outside). The remaining five holes can then all be reamed out until the tape stops the reamer from going any further. Be careful when drilling or reaming Perspex, by the way. It can easily crack if the drill or reamer is forced into the hole. If using the original lid, the rectangular cut-outs can be made by drilling a series of small holes inside the perimeter, then knocking out the inside piece and filing to shape. Make sure that the large cut-out is exactly the same size as the Perspex window so that the latter is a tight fit. The window can be secured in place using a few spots of contact adhesive. The rear of the box has to be drilled for LEDs4-6, while a pattern of 5mm holes is also required for the loudspeaker. In addition, a hole is required in the righthand end of the case to provide access to the DC socket and on/off switch (these holes go in the end of the case adjacent to the 10mm LED holes). Front-panel label The front-panel label is available in PDF format on the SILICON CHIP website. It’s just a matter of downloading it and printing it out onto an A4 sized synthetic Dataflex or Dataplex sticky label (see panel). This label can then be attached to the lid and the holes cut out using a sharp hobby knife. Alternatively, you can print out a paper label and attach this to the lid using double-sided tape. An additional label (Fig.1) shows the function of each of the buttons on the handheld remote and this is affixed to top panel of the case (see photos). Final assembly Now for the final assembly. The first job is to mount the PCB assembly on the lid (or Perspex panel) using M3 x 15mm spacers and eight M3 x 6mm machine screws. Once that’s done, the AA cell holder can be secured inside the case. This is mounted against the base of the box and is secured to the top panel using a No.4 x 9mm selftapping screw. siliconchip.com.au The view inside the completed prototype. The battery holder is secured to the top of the case using a No.4 x 9mm self-tapping screw that goes into a slot at one end of the holder’s plastic moulding. Drill a 3mm hole for this screw in the top panel exactly 77mm from the righthand side of the case and 38mm from the front (as measured without the lid). The self-tapping screw is then fed through this hole and goes into one of the slots in the end of the cell holder’s plastic moulding. The last part to go in is the loudspeaker. It’s just a matter of securing it in place on the rear panel (ie, the base of the box) using a suitable adhesive such as super glue, contact adhesive or neutral-cure silicone. Smear the glue around the perimeter of the speaker frame, then centre it over the holes made in the base of the box and wait for the adhesive to set. The speaker is then connected to the 2-way screw terminal block on the PCB using figure-8 cable. Testing Now for the smoke test. Check that IC1 is out of its socket, then apply power and check that the voltage between TP +12V and TP GND (ie, between pins 14 & 5 of IC1’s socket) is 5V. Note that this reading can be anywhere between 4.75V and 5.25V, depending on the regulator. If this is correct, switch off and install IC1 into its socket, taking care with its polarity. That done, reapply power and check that the displays show 0:0 but with DISP1 unlit. This unlit digit is due to the leading zero blanking that’s incorporated in the tim-   Dataflex/Datapol Labels (1) For Dataflex labels, go to: www.blanklabels.com.au/index. php?main_page=product_info& cPath=49_60&products_id=335 (2) For Datapol labels go to: www. blanklabels.com.au/index.php? main_page=product_info&cPath =49_55&products_id=326 December 2015  77 Parts List: Speech Timer 1 double-sided PCB, code 19111151, 162.5 x 102mm 1 front panel label, 195 x 110mm 1 remote control button function label, 23 x 64mm 1 UB2 plastic case, 197 x 113 x 63mm 1 9-button IR remote control (Little­ Bird Electronics, SparkFun SFCOM-11759) 1 CR2025 3V alkaline cell 1 141 x 68 x 3mm transparent red acrylic or red Perspex sheet (or 195 x 110mm – see text) 1 PCB-mount vertical slider switch (Altronics S2071) (S1) 1 8-AA cell holder or 2 x 4-AA holders (optional) 8 AA alkaline, NiMH or Nicad cells (optional) 1 12V DC 400mA plugpack (optional) 1 2.5mm or 2.1mm PCB-mount DC socket (CON1) 1 2-way screw terminal block, 5.08mm pitch (CON2) 1 76mm 8Ω loudspeaker er. DISP1 should light up only when it is required to display anything other than zero. Check that the blue acknowledge LED flashes when using the infrared A hole is cut in the righthand end of the case to provide access to the DC socket & on/off switch. 78  Silicon Chip 1 20MHz parallel resonant crystal (X1) 1 DIP18 IC socket 3 DIP14 IC sockets cut into 6 x 5-way SIL socket strips 4 M3 x 15mm tapped Nylon spacers 9 M3 x 6mm screws 1 M3 nut 1 No.4 x 9mm self-tapping screw (when 8-AA cell holder is used) 1 100mm length of medium-duty figure-8 wire 11 PC stakes 1 210mm length of 1mm-dia. tinned copper wire 1 150mm length of 2mm-dia. heat­ shrink tubing Semiconductors 1 PIC16F88-I/P microcontroller programmed with 1911115A.hex (IC1) 1 4051B single-pole 8-way analog switch (IC2) 1 ULN2003 7-Darlington array (IC3) 1 7905 negative 5V regulator (REG1) 9 BC327 PNP transistors (Q1-Q9) 1 BC337 NPN transistor (Q10) remote. Further operation can then be tested using the remote control, as set out in the following section. Remote control We’ve already briefly mentioned the SparkFun remote and its button functions. Let’s now take a look at the 5-button array below the A, B & C buttons and describe how they control the Speech Timer. The left arrow button is for Reset – it stops and resets the clock timer to zero. In this state, the Up and Down buttons can be used to scroll up or down through the preset timer selections. These selections include the 0:0 setting and the presets 1-2, 2-3, 3-5, 5-7, 10', 15' and so on up to 90' (the ['] symbol indicates minutes). Pressing the right arrow button (Start) starts the timer running. It starts with 0:0 displayed and the colon flashing at a 1-second rate. The central “O” button is the Pause button and is used to stop the clock, so that it ceases incrementing. When paused, the colon stops flashing to indicate that it is in this mode. Pausing is useful for stopping the Speech Timer after the contest so that 3 58mm 7-segment displays (Jaycar ZD-1850) (DISP1DISP3) 2 waterclear red 2000mcd 10mm LEDs (LED1,LED4) 2 waterclear amber 9000mcd 10mm LEDs (LED2,LED5) 2 waterclear green 13000mcd 10mm LEDs (LED3,LED6) 1 3mm blue LED (LED7) 1 TOSOP4136 38kHz IR receiver or similar (IRD1) 2 1N5819 1A Schottky diodes (D1,D2) Capacitors 1 470µF 25V PC electrolytic 5 10µF 16V PC electrolytic 2 100nF MKT polyester 2 33pF ceramic Resistors (0.25W, 1%) 3 4.7kΩ 4 330Ω 1 2.2kΩ 1 180Ω 2 1kΩ 1 100Ω 9 470Ω 7 82Ω 1 15Ω 1W 5% (optional – see text) the overall time can be read off the display (and written down if necessary). The timer can then resume from that time by pressing the Start button or reset back to zero by pressing the Reset (left arrow) button. Note that there is only a single “seconds” digit on the timer display and this normally only shows the tens of seconds. It increments by one each 10 seconds when the clock is running. The exact seconds value can be viewed by pressing the Up or Down button. For example, let’s say that the display shows 12:4 (ie, 12 minutes and 40 seconds). Pressing the Up or Down button then causes the display to show the exact number of seconds, eg, 43'' (ie, 43 seconds). This was only partially displayed as the 4 in the 12:4 display. Note that the [''] after the 43 is the symbol for seconds and the exact number of seconds is only displayed while the Up or Down button is held pressed. Note also that the seconds only show when the timer clock is running or when it is paused but not when reset. The seconds are reset to zero when the unit is reset (left arrow button) and the Up and Down buttons are siliconchip.com.au A pattern of 5mm holes is drilled in the rear panel for the loudspeaker, while an artwork showing the remote control functions is attached to the top panel. then instead used to select one of the timer presets. Additional buttons The SparkFun remote’s power button is used to adjust the brightness of the 7-segment displays (DISP1-DISP3). These displays can be dimmed up or down, with the dimming direction changed each time the button is pressed. Pressing and holding the but- ton begins dimming in either direction. The remote’s “B” button is used to independently adjust the Brightness of the indicator LEDs in the same way as the power button. The “A” button serves two functions: (1) to manually sound the alarm and (2) to set the volume. If this button is pressed for more than five seconds, it operates as a volume control. After this time, the normally modulated Using The Speech Timer In Count-Down Mode Normally, all times set for the Speech Timer, whether preset or manual, are in Count Up mode, eg, a 10-minute speech will start from zero and count up to the set time, at which point the red warning LED will come on. But the counter will continue to run after that and if the speech was being given at a Toastmasters’ meeting, there is a risk of disqualification if the speech runs for another minute or more (whatever the rule). In addition, the Speech Timer can also operate in Count Down mode. In this case, for a 10-minute speech (say), the Speech Timer will start at 10:0 minutes and then count down in 10-second decrements to zero. At zero, the buzzer will also sound briefly. To access the Count Down mode, you simply press the Up button on the remote repeatedly until you get a display of 0:0. Further presses of the Up button then increase the timer setting from 0:0 to 0:1 and so on up to 99:5 (ie, 99 minutes and 50 seconds). siliconchip.com.au Once the timer setting is above 0:0, the remote’s Down button can be used to decrease the setting if necessary. In operation, the Up and Down buttons increase/decrease the timer setting in single step with each button press. Alternatively, holding down a button will cause the timer value to rapidly change up or down. Once the timer value has been set, pressing the Start (right arrow) button) will cause the timer to start counting down to 0:0. When it reaches 0:0, the timer will stop and the buzzer will automatically sound for 2.5s. The previous Count Down timer setting can then be restored by pressing the Reset (left arrow) button. Warning LEDs The warning LEDs can also be preset. That’s done simply by selecting a warning LED with the remote’s “C” button. The selected LED can then be programmed to turn alarm tone becomes continuous, indicating that the unit is in volume setting mode. The “A” button then has to be released and repressed within 1.25 seconds. When that’s done, the modulated alarm tone is restored and the volume begins to change. If the volume is changing in the wrong direction, it’s just a matter of releasing and repressing the “A” button once more. The volume will then change in the opposite direction. The volume will continue to change for long as you continue pressing the button until it reaches its maximum or minimum level. Releasing the “A” button for more than 1.25s exits the volume setting mode and this will be indicated by a brief “chirp” from the loudspeaker. The alarm (A) button will then operate as normal unless pressed again for longer than five seconds. The “C” button cycles through the warning LED indicators, starting with all LEDs off and then lighting the green LED, then the amber LED and finally the red LED in a cyclic fashion for each press of the button. Finally, note that the timer presets, display brightness and volume settings are stored in EEPROM and are retained when power is switched off. This saves you from having to re-enter the setting each time power is reapplied. That’s it – your Speech Timer is SC ready for action. on at a certain time during the count down using the Up & Down buttons. You can program each warning LED but note that you need to select the next LED using the “C” button before changing the time setting. Note also that, during the count down, you need to have the green LED light before the amber LED which in turn lights before the red LED. This means that it’s best to program the green LED first, followed by the amber LED and then the red LED, each with a progressively lower time setting. The warning LED programming an be cancelled by setting the timer to 0:0 and then cycling through each LED with the “C” button. Restoring count up timing Pressing the Down button when the timer is at 0:0 re-selects the preset periods, starting with 90', then 80' etc. This resets the Speech Timer to function as a Count Up timer and the presets can then be selected using the Up and Down buttons. December 2015  79