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Don't get caught with an overflowing bin Build the garbage reminder Did you for get to put out the garbage this week? Isn't it frustrating? There you are with an overflowing bin and nowhere to put the excess. You can avoid that problem in the future by building our Garbage Reminder. It will flash a reminder to you on each garbage night. By JOHNNO 'BLUE SINGLET' CLARKE While not the most life threatening problem presently confronting the planet, forgetting to put out the garbage is a pain. Either you remember next morning when it is far too late or perhaps you remember at the very last minute and have to sprint after the garbage truck dressed in your slippers and "jarmies". Have you heard the joke about the little old lady who remembered to put out the garbage at the very last minute? Calling out to the garbage collectors, she said, "Am I too late?" "No luv, jump in." She needed our Garbage Reminder, didn't she? Our Garbage Reminder is a small battery powered unit which has a flashing LED to indicate when it is garbage night. When you've put the The Garbage Reminder is battery powered and will flash a LED for 7 hours whenever it's garbage night. To turn the LED off, just press the "BIN OUT" switch in the middle of the truck. 48 SILICON CHIP bin out, you then press the BIN OUT switch to stop the LED flashing. You can set the Garbage Reminder to flash the LED on any evening of the week. Say your garbage nights are Monday and Thursday. Just set the Garbage Reminder to flash the LED on those nights and you will never have a garbage debacle again. Of course, you need to put the Garbage Reminder where you will see it before you go to bed. You could stick it to your fridge door, bathroom mirror, bedside table or whatever. Now you might wonder why we would bring the full engineering talents of SILICON CHIP engineers to bear in solving a trivial problem like this but think about it. It is not all that easy to solve. You need a timer which can be set to flash a LED on any one or two (or more up to seven) nights a week and it must do it accurately. You don't want to have to reset it every month or so, do you? Furthermore, it must provide an effective reminder and run very economically from batteries. Naturally, it can't run on mains power because a blackout might upset the timing and then where would you be? You might put the garbage out on the wrong night! So that sets the circuit requirements. It must be accurate, battery operated and economical. That means it must be crystal controlled, run from CMOS ICs and have a very low current drain. The batteries should last around a year. or more. Naturally, while we have presented the timer as a Garbage +3V 16 16 32.768kHz 10 10 16VW .,. + - 10M 1------.. +8640 - - - - - ----l POWER ON RESET +3V 100k .,. 10CYCLES/24HRS + +3V .01 i 16 R 15 IC& 4017 +10 co n D 8 IC7 4017 +7 ICYCLE124HRS 13 7 ..I. R 15 3 8 13 .,. .,. 01 100k .,. 1M .001+ 11 2.2k LED1 . . - - - - , 6 A 1' ICB LM3909 K 100 6 F2_\-IVll-~---1' 8 EOc .,. VIEWED FROM GARBAGE REMINDER Fig.1: the circuit uses a readily available 32.768kHz watch crystal as the timebase. This is divided down by IC2, IC3, IC5, IC6 & IC7 to obtain a weekly cycle. The DIP switch (S1) selects the days while IC8 flashes the LED. Reminder it could be used to remind you of other tasks such as taking daily medication (the pill?], feeding the goldfish or remembering to go to work (or better still, when to stay home]! Space age styling In line with the fairly prosaic nature of the task it is supposed to remind you to do, the Garbage Reminder has pretty ordinary looks. It is just a plastic box with a light emitting diode and a pushbutton on it. There is no on/off switch (you don't want anybody inadvertently switching it off] and there is no visible means of setting it - that's inside. We have provided an interesting front panel label though, with a picture of a garbage compactor truck on it. Like it? Inside the case is a miniature 8-way DIP (dual inline package) switch. Seven of these switches are used to nominate the days you want to be reminded to put the garbage out. Switch 8 doesn't do anything. How do you set the Garbage Reminder? Easy. Say it's 5 o'clock on Monday and tonight is garbage night and so is Thursday night. OK. Set switches 1 and 4 to the ON position and all the others off. Now connect the batteries and the LED will AUGUST 1989 49 POLYESTER & CERAMIC CAPACITORS No. □ □ □ □ □ □ □ 1 2 1 1 1 1 1 Value 0.1µF .047µF .01µF .001 BµF .001µF 33pF 10pF IEC 100n 47n 10n 1n8 1n 33p 10p EIA 104K 473K 103K 182K 102K 33K 10K RESISTORS No. □ □ □ □ □ 1 4 3 2 1 Value 10MO 1MO 220k0 100k0 2.2k0 start flashing at the rate of about once every two seconds. It will continue to flash for 7 hours 12 minutes unless the BIN OUT switch is pressed. That's all you have to do. The Garbage Reminder will now continue to work until the batteries go flat which should be at least 12 month's away. More likely, we expect alkaline cells to last around 2 years or so. Circuitry The Garbage Reminder -uses 8 CMOS !Cs, plus a few diodes, a crystal, a LED and some resistors and capacitors. The !Cs are all low cost devices and draw very little current which makes them suitable for battery operation. Why so many !Cs? We had to use readily available parts and a cheap and readily available quartz crystal to give an accurate time reference. Therefore we used a 32kHz watch crystal which is just about the cheapest type you can get. The precise crystal frequency is 32.768kHz. This has to be divided down by a factor of 1.9818 x 1010 to obtain a weekly cycle. That sounds like a huge division ratio and so it 50 SILICON CHIP 4-Band Code (5%) brown black blue gold brown black green gold red red yellow gold brown black yellow gold red red red gold 5-Band Code (1%) brown black black green brown brown black black yellow brown red red black orange brown brown black black orange brown red red black brown brown is. Let's see how it is achieved. NAND gate IClc (4011) operates as the crystal oscillator. It is biased with lOMO and 220k0 resistors so it functions as a high gain inverting amplifier. The 32kHz crystal is connected across the lOMO resistor while the lOpF and 33pF capacitors provide the correct loading for it. The square wave output of IClc is a 32.768kHz signal which may appear to be a strange oscillator frequency to use for a clock circuit. In fact, 32,768 is 215. Following IClc is IC2, a 4020 14-stage binary divider. Its output at pin 3 (Q14) is a square wave at 2Hz. There is also a test signal at the Q4 output (pin 7) at 2.048kHz but more on that later. The 2Hz signal from IC2 is fed to IC3 which is another 4020 14-stage binary counter. Together with 4-input AND gate IC4 and JK flipflop IC5, IC3 provides a division ratio of 8640. This results in an output at pin 15 of IC5a of 20 cycles per day. How do IC3, IC4 and IC5a provide a division by 8640? There are four outputs taken from IC3 and these are Q7, Q8, Q9 and Q14. The Q14 output goes high after 8192 counts, Q9 goes high 256 counts after Q14 goes high, Q8 goes high 128 counts after Ql4 goes high and finally Q7 goes high 64 counts after Q14 goes high. When all these outputs are connected to the 4082 4-input AND gate, IC4, the output goes high after the sum of 8192 + 256 + 128 + 64, or 8640. Further, the pulse from IC5a is divided by two to provide a square wave at the rate of 10 cycles per day. This 10 cycles per day output is then fed to IC6, a 4017 decade counter/divider which gives out one positive-going pulse (lasting 12 hours) every 24 hours from its output at pin 12. This one pulse per day output is fed to IC7, another decade divider and its outputs are fed to the "day select" DIP switch Sl. Diodes Dl to D7 isolate each of the "day" outputs so that they don't load each other if more than one day per week is selected. The selected day outputs from the DIP switch are fed to NAND gate ICld together with a 2.4-hour pulse output from pin 3 of IC6. ICld's output is then fed to an RS flipflop consisting of IC la and !Cl b. The output of this flipflop, at pin 3, is turned on PARTS LIST 1 plastic case , 130 x 67 x 43mm (Altronics Cat. H0153) 1 front panel label, 125 x 64mm 1 PCB, code SC081 08891 , 105 x 60mm 1 8-way DIP switch 1 momentary contact pushbutton switch 1 battery snap connector 1 2-cell AA battery holder (Jaycar Cat. PH-9202) 2 1.5V alkaline AA cells 1 32 . 768kHz miniature (watch) crystal Semiconductors The assembled PC board simply clips into the bottom of the specified plastic case. Power comes from two 1.5V alkaline AA cells. The DIP switch is used to set the nights that the LED is to flash. To select each night, just slide the corresponding slider to "ON" (see text). (set) by the output of ICld; and pin 3 is pulled low (reset) when the ' 3' output of IC6 goes high and is inverted by transistor Ql. Similarly, the flipflop can be reset early by pressing the BIN OUT switch, S2 . RS flipflop IC1a/IC1 b actually powers IC8, an LM3909 LED flasher . This causes the LED to flash at a rate of about once per se- cond, depending on the condition of the batteries. So what happens is that, when one of the day outputs from IC7 goes high, the RS flipflop allows the LED to start flashing when the 'O' output (pin 3) of IC6 goes high. The LED then stops flashing 7. 2 hours later, when the flipflop is reset by the ' 3' output of IC6. That is, unless you put your garbage bin out and then remember to press the BIN OUT switch. To ensure that all the counter ICs in the circuit operate correctly when power is first applied, they are all reset automatically. For IC2 to IC7, all the reset pins are connected to the junction of a 10µ,F capacitor (the other side of which is connected to the positive supply] and a 100k0 resistor to ground. When power is first applied, the 10µ,F capacitor is discharged and so it effectively pulls the reset line to the positive supply, resetting IC2 , IC5a, IC5b and IC6 directly and indir ectly, IC3. IC3 is reset when the Ql output of IC5a goes high at the power on reset. Once the 10µ,F capacitor charges, the power on reset line goes to ground and normally counting can take place. 1 4011 quad 2-input NANO gate (IC1) 2 4020 14-stage counters (IC2, IC3) 1 4082 dual 4-input AND gate (IC4) 1 4027 dual JK flipflop (IC5) 2 4017 decade counter/dividers (IC6, IC7) 1 LM3909 LED flasher (IC8) 8 1 N914 diodes (D1 to D8) 1 BC54 7 NPN transistor (Q1) 1 5mm high brightness LED Capacitors 1 1 1 1 2 1 1 1 1 1 100µ,F 16VW PC electrolytic 4 7 µ,F 16VW PC electrolytic 1 Oµ,F 16VW PC electrolytic 0 .1 µ,F metallised polyester (greencap) .04 7 µ,F metallised polyester .01 µ,F metallised polyester .0018µ,F metallised polyester .001 µ,F metallised polyester 33pF ceramic 1 OpF ceramic Resistors (0 .25W, 5%) 1 10MO 4 1 MO 3 220k0 2 1 OOkO 1 2.2k0 Miscellaneous Tinned copper wire for links, hookup wire for switch, solder, etc . IC7 has its own power-on reset network, consisting of a .01µ,F capacitor and 100k0 resistor. IC7 is also reset at the end of a 7-day period when pin 6 goes high. This is connected to pin 15 via D8 and thus resets IC6 so that all outputs are low. AUGUST 1989 51 penetrate the front panel. Finally, wire up the BIN OUT switch and the battery clip leads. The circuit is now ready for testing. Testing o 1111 F I ~ I I ""-.........._ ....____.o_a_1_oa_s_9_1_ ...._, Fig.3: here is an actual size artwork for the PC board. GARBAGE REMINDER BIN OUT Fig.4: in keeping with the styling, the front panel features a garbage compactor truck. You'll never forget the garbage again. The whole circuit is powered from two AA cells in series, giving 3V. We recommend the use of alkaline cells for longest battery life. By the way, the circuit will work with the battery voltage down to below 1.8 volts. Construction The Garbage Reminder is built into a standard plastic case measuring 130 x 67 x 43mm (Altronics Cat. H-0153). All the circuitry is mounted on a printed circuit board measuring 105 x 60mm (code SC08108891). Begin construction by carefully inspecting the printed circuit board tracks for opens and shorts between tracks. The PCB is designed to sit in the base of the specified case on the integral supports. Make sure the board is a neat fit into the case 52 SILICON CHIP before you assemble any components onto it. Start assembly of the PCB by inserting and soldering in the links and resistors. Do not install Link 1 at this stage. Install Link 2 instead. This is done for initial testing of the circuit and makes it run 1024 times faster than normal. Next install diodes D1 to DB making sure that they all point in the same direction (band ends closest to IC3). The ICs can go in next and they are all oriented in the same direction. Check that each IC is correctly in place before soldering. When installing the DIP switch make sure that it is oriented so that switch 8 is closest to the diodes. This done, install the capacitors, crystal and LED. The LED is mounted with the leads long enough (say about 22mm) so that it can just Firstly, set DIP switches 1 to 7 to the "on" position. Switch 8 can be set either way since it is not in circuit. This will cause the LED to flash on every day. Now insert the two AA cells into their holder to power up the circuit. The LED should then flash at about once a second for about 25 seconds (yep, that means it should flash about 25 times). 59 seconds after it stops flashing, it should flash again, for 25 seconds. What is happening is that each day's cycle has been speeded up by 1024 times so that a 24 hour period is simulated in 84.375 seconds. Knowing that, you can check that the unit cycles correctly for any combination of days set by the DIP switch. Note that each time you change the DIP switch settings, you need to remove the batteries and short out the battery snap connector so that the circuit is properly "powered down". If you don't do this, the circuit won't properly reset itself. Powering up should always start the circuit timing from day 1. You can also check the function of the BIN OUT pushbutton - does it stop the LED from flashing? Once the circuit operation is proven, link 2 can be rerp.oved and link 1 inserted. The Garbage Reminder will now operate over a 7 day cycle. Installation The front panel label can be fixed to the plastic lid and a 5mm hole drilled for the LED. This hole should be positioned so that the LED becomes the rear flasher of the garbage truck logo on the panel. The switch cutout is located just below the BIN OUT labelling. Now clip the PCB into place and check that the LED penetrates through the lid sufficiently. Adjust the height of the lid as necessary if you encounter problems at this step. The Garbage Reminder is now complete and all that is left to do is to set the DIP switches. continued on page 79 banana jacks for the vertical input connections then PLl must be a banana plug. Adjustment (b) (a) FIG.11: IMPROPER ADJUSTMENT of Cl will produce the rounded leading edge shown in (a) or overshoot of the leading edge as shown in (b). Ideally, PLl should be a BNC connector but some scopes may require the use of a banana plug connector. Bear in mind that, as shown in Fig.6, a BNC connector provides full shielding all the way from the probe to the scope's input, while a banana plug actually breaks the shield at the connector and will allow some noise pickup. For example, on a square wave signal, a BNC connector gave a rock-steady trace as shown in Fig.7a. In Fig.7b, PLl was a banana Garbage Reminder ctd from page 52 To set the unit, all you need to do is insert the batteries at the time you want the LED to begin flashing on your garbage collection day or days. The LED will flash for 7 hours and 12 minutes unless stopped using the BIN OUT switch. Normally the reminder would be set to start the LED flashing at about 5pm or 6pm. It does not matter which day the batteries are inserted since the days are selected using the DIP switches. Day 1 is the day that the Reminder is set, day 2 the next day and so on. For example, if the Reminder has its batteries inserted on Wednesday at 5pm, day 1 is Wednesday and day 7 is Tuesday. If your garbage night is Sunday and Wednesday, the required settings are switches 1 and 5 on. All other switches are off. Got it? Good. Now get that garbage out! ~ plug that was connected to a BNCbanana adaptor. Notice that noise (hum) pickup has caused the trace to "smear" . Fig.7c is the same trace as Fig.7b but a faster camera shutter was used to show that the "smear" is actually another signal (60Hz mains signal leaking through the broken shield at the banana plug) that is superimposed on the square wave. So if possible, maintain shielding throughout the entire assembly. Of course, if your scope only has To adjust the probe, set the scope's vertical input for DC. Then, using any known good square wave as the signal source - lkHz is almost a universal standard - use an insulated alignment tool to adjust Cl for the precise square wave shown in Fig.7a. Improper adjustment of Cl will result in a rounding of the signal's leading edge (Fig. 11 a) or overshoot of the signal's leading edge (Fig.llb). Refer to the scope probe article in the June issue to learn why Cl 's adjustment does what it does. Finally, be sure to allow for the x 10 factor when using the low-C xlO probe. For example, if the scope indicates that a signal is 1.1 volts p-p, then the actual value is 11 volts p-p. ~ Copyright 1989, Gernsback Publications. Reprinted with permission from January 1989 Radio-Electronics. 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