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BASICS!-how can i make this simple recorder loop?

Hi and forgive my ignorance! im absolutely new to electronics but am enjoying building kits and playing with pre-fab circuits, trying to understand them. my query is about a simple 10-second voice recorder kit i came across that came pre-built :( but plays the recording only once. to play the recording, there is a contact that needs to be broken, and then the whole recording will play once. there is what i assume to be a small IC under a black blob in the middle of the circuit board. the whole thing is powered off 4 watch batteries.

im wondering if there is a simple (ish) solution to being able to make the recording loop on playback.

the only thing i could think was that i would need to somehow send a pulse or something every ten seconds to the contact.... then i thought maybe it had something to do with the capacitors.... then i looked at the blob.... then i found you :).

if anyone has any suggestions for a curious lad, i would be very appreciative....

the kit can be seen at:

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Thanks in advance,

arthur.

Reply to
arthur byte
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On Wed, 08 Nov 2006 04:05:54 -0800, arthur byte wrote: ...

...

I'm afraid your idea of just triggering it every 10 seconds is probably the only way you're going to accomplish this. But a 10-second astable is pretty simple to do with, say, a CMOS 555 (you want CMOS because of the current consumption), and _PROBABLY_ could just go straight from the

555 output to the switch input, but I'd scope it out first.

How do you record on it? Is there another button?

Good Luck! Rich

Reply to
Rich Grise

Hi, Arthur. Mr. Grise's suggestion of using a CMOS 555 is a good one. You can probably get all the parts from Maplin.

The ISD chips use a contact to circuit GND to start the playback loop. Use a DMM (if you've got one) to measure the voltage at the two wires of the strat switch. The lower voltage is circuit common or GND (call it Wire 2), and the higher of the two voltages is the input (call it Wire 1).

Now you need to cobble together a 555 with an NPN transistor like a

2N3904 to do this (view in fixed font or M$ Notepad):

| | VCC VCC VCC | + + + | | | | | .-. | | | 150K| | .---o----o---. | | | | 8 4 | | '-' | | | | | | | o-----o7 | | | | | Wire 1 | .-. | LMC555 | .------->

| 10K| | | | | | | | .--o6 | | | '-' | | | ___ |/ | | | | 3o---|___|--| 2N3904 | o--o--o2 | 22K |>

| +| | 1 5 | | Wire 2 | --- '---o----o---' o------->

| --- | | | 100uF| === === | === GND GND | GND | (created by AACircuit v1.28.6 beta 04/19/05

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This should turn on the transistor (and restart the ISD chip about once every 10.5 seconds or so. Depending, it might be better to use a 180K or 220K resistor in place of the 150K -- your call. Don't make it too close -- cap values drift over time and with temperature.

The easiest way to supply power would be to just use an external 9V alkaline battery for the 555/transistor circuit. That way you don't drain the little coin cells, which look like they might be a little difficult to replace.

Good luck Chris

Reply to
Chris

im not sure that i unerstand this diagram, but i managed to find a great explanation of these 555 ics (for other complete beginners, go here:

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im going to try and use the information you gave me (thank you thank you thank you!) and combine it with the simpler diagrams in the link. and having looked at the link above, im beginning to get a better understanding of your diagram.

thanks again,

a-

Reply to
arthur byte

Hi, Arthur. The 555 page you referenced does have all the basics. If you use a 9V transistor battery, have the output of the 555 drive an NPN transistor (whose emitter is tied to the 555 common/9v battery -), and then connect the collector of the transistor to the higher voltage switch wire and the emitter to the lower voltage switch wire, you should be fine.

ASCII schematics have been on newsgroups for a long time. Since you're a Google Grouper (as am I), you might not know you have to look at the ASCII diagram in a non-proportional font like Courier for it to make sense. In order to see the diagram, click "Show Options" on the Google message header, then click "Show Original", and see it in all its ASCII splendor. ;-)

Cheers Chris

Reply to
Chris

Hi Chris,

thanks for the information. your diagram makes great sense now!!

i appreciate all your help. this little project is actually turning out to be a great method of learning electronics.

is it possible to put a variable resistor in the circuit to be able to control the length of the loop or does that open up a whole new can of worms?

thanks,

a-

Reply to
arthur byte

Sure. Just replace the 150K resistor with a 100K resistor in series with a 100K pot, and you'll be able to tweak it in pretty well.

Again, make sure you leave a half ssecond or so between the end of the loop and the beginning of the next. That'll allow for any slight drift of the cap value over time and temp.

Good luck Chris

Reply to
Chris

You can use variable resistors wherever you want to, as long as you remember not to crank them down so low that they short something out.

If you look at the charge and discharge current paths, you can make it do even more tricks, if you use a couple of diodes.

The cap charges through Ra+Rb, but only discharges through Rb, but you can stick some steering diodes in there and make the duty cycle pretty much whatever you want, within limits. (which I've never tried to find - what I had has always been good enough.)

Oh, yeah, and put at least 1 nF from pin 5 to ground. Pin 5 is the control voltage, and if you're not using it to do FM, then it needs to be bypassed.

Have fun! Rich

Reply to
Rich Grise

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