DEX PRODUCTS HEARTBEAT SIMULATOR for baby's crib

[jamiewoody]

i did some experimenting on a DEX baby heartbeat simulator, which you place in a baby's crib.

i found, if i connect a resistor to the potentiometer which controls the volume, it lessens the volume.

it ALSO slows down the heartbeat.

now, i wonder if i were to wire a potentiometer between these two leads, could that control the "heartbeat"?

[jamiewoody]

being a very simple circuit, i discovered a couple of more bends.

jumping another resistor to a different resistor on the potentiometer, i found it makes the BEAT more trebbly , a little more distorted and faster.  using the same resistor and clipping the next lead on the potentiometer, it becomes slower and a little more distorted.

so, perhaps i could have a little drum machine here?

[Gordonjcp]

What's inside it?  Is it a "black blob" device or is it a little board with discrete components so you could possibly trace out the circuit?

[jamiewoody]

6 resistors,2 diodes, 2 caps and a potentiometer.  a very basic circuit. 3 volts.

the newer models appear to be much more sophistocated.

i am still LEARNING some basic electronics. i have a very basic working knowledge, and a lot to learn. mine is a "monkey see monkey do" type of method so far.

i am not sure of a model number for this. if i disconnected the tiny speaker and wired a jack, plugged it into an amplifier, it would sound bassier, which could be cool.

there is a lot that can be experimented with here. i could change the phase of the speaker wires.

for such a simple circuit, it is amazing what i have come across so far.

[marmora]

I found one of these in the trash recently.  Mine has a black blob on the side opposite the main through-hole components.
There's a 1M resistor that controls the speed/pitch of the heartbeat.  You can sub it for a large value pot or add contacts etc.
My only issue with this is that when I add an output jack in place of the speaker along with a 8ohm (In my case I used 12ohm since that's what I had) resistor across the lugs, the resistor gets very hot.  I'm using a 1/4 watt resistor.
Should I be concerned or not?

[Circuitbenders]

It might be better to use a ceramic power resistor if you're concerned about it getting hot. They'll probably be rated at around 6 watts or something similar.

Do you actually need a dummy load there?

[marmora]

Not too worried about it as long as there are no long term problems.  It's unusual though.
Yeah, it does need the dummy load.  I was a little surprised.
Thanks for the idea.

[Gordonjcp]

It shouldn't get *that* hot.  That suggests it's dissipating well over quarter of a watt, which is about twice as much as one of those crappy unamplified iPod speakers at full volume.  If it gets a 12 ohm resistor hot, it must be absolutely guzzling batteries.  Are you sure you've wired it up exactly the way the speaker was wired?