{"id":5604,"date":"2013-01-02T09:20:05","date_gmt":"2013-01-02T17:20:05","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=5604"},"modified":"2013-01-16T18:07:12","modified_gmt":"2013-01-17T02:07:12","slug":"2013-01-02-ticking-time-bomb","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=5604","title":{"rendered":"2013-01-02 “Ticking Time Bomb”"},"content":{"rendered":"

\"\"<\/a>Remember Capt. Hook and the crocodile?\u00a0 This circuit is almost the same as a flasher, except instead of an LED it uses a speaker.\u00a0 The result is that it pulses the speaker with a very short pulse of\u00a0 current.<\/p>\n

The circuit uses a 9V battery, but today the 9V battery is too expensive, so I would replace the 9V battery with a single AA cell and a Joule thief to boost the voltage up to about 4 to 6 volts.<\/p>\n

The circuit could be changed to a flashing Joule Thief so that the transistors\u00a0 that do the flashing also boost the voltage.<\/p>\n

Update Jan 5<\/h3>\n

I built the circuit on a piece of wood with some tiny screws as the solder points.\u00a0 I made a few changes to it as follows.\u00a0 I changed the BC557 PNP to a SS8550 1 amp audio output transistor.\u00a0 I changed the BC547 to a PN2222A.\u00a0 I changed the 2.2 uF electrolytic to two 1 uF monolithic ceramic capacitors in parallel.\u00a0 I changed the 200k pot to a 600k pot.\u00a0 Instead of 9V, I set the power supply at 4.5VDC, which seemed to be loud enough.<\/p>\n

I powered it up and found that it did, indeed, tick like a time bomb.\u00a0 I could vary the tick rate from less than 1 per second to a low buzz of maybe ten per second.\u00a0 But the current on the power supply’s meter was too low to read, so I put the DMM in series with the power supply lead.\u00a0 The meter would read zero until a click, then jump up a little bit, but it wasn’t readable.<\/p>\n

To get a stable reading, I put a 10 thousand uF capacitor across the time bomb’s supply leads, and a 100 ohm resistor in series with the positive lead.\u00a0 This filtered out the spikiness of the supply current.\u00a0 When I adjusted the click rate for about 2 a second, the current was under 2 milliamps at 4.5V.\u00a0 When I increased the click rate, the current went up to about 5 milliamps.<\/p>\n

That current is so low that it would run for a week or more using three AAA cells.\u00a0 It would be really easy to run it using a single AA cell.\u00a0 If I want to keep the circuit as it is, I would have to add a Joule Thief to convert the 1.5V to 4.5V.\u00a0 That’s easy to do, since the average output current would be 5 milliamps or less, so accounting for efficiency, the JT would draw about 30 milliamps at 1.5V from the AA cell.\u00a0 The output of the JT is rectified and filtered, and a 4.7V zener would be used as a shunt regulator.\u00a0 The time bomb would then be connected across the zener.<\/p>\n

The only thing that I don’t like about this is that the shunt regulator wastes most of the power.\u00a0 I could redo the JT so that it is shut down when the voltage gets up to 4.5V, so between clicks, it doesn’t waste much power.\u00a0 But this just adds more complexity to the circuit that already is getting complicated.\u00a0 A better way to go would be to make a flashing Joule Thief, but instead of an LED, it drives a speaker.\u00a0 The circuit itself does the conversion along with the<\/p>\n

Tick.. Tick.. Tick..<\/p>\n

Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":"

Remember Capt. Hook and the crocodile?\u00a0 This circuit is almost the same as a flasher, except instead of an LED it uses a speaker.\u00a0 The result is that it pulses the speaker with a very short pulse of\u00a0 current. The circuit uses a 9V battery, but today the 9V battery is too expensive, so I <\/p>\n

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