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PCB design question

Hi, I hope you can help me.

I just bought a Homedics WC-100 Envirascape Indoor Electronic Wind Chime unit that turns a small fan on at intervals that causes chime rods to make sounds. The "O" button on the units front is power on/off, and the "-" and "+" buttons decrease/increase the interval of the fan. It's powered by a 6VDC 120mA brick.

My problem is that it has a feature that turns the unit off after one hour of use, which I do not want. - I want it to stay on until I manually turn it off - either by units switch, or if needed, by a line cord switch.

Pic links noted below are of the unit and PCB, and hope you can help me in determining a simple task I can do so as to not have it auto-turn-off. Maybe cutting a circuit, or jumping a circuit?

Homedics won't tell me for liability issues - I guess if they tell me what to do, and it burns up, with my office, they'll be liable. :-(

Maybe you can reverse engineer the PCB - it looks like a very simple one. Your help will be much appreciated.

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Reply to
anonacct69
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That's what I thought too, but you could use the motor turning off to trigger a 555 one-shot "pressing" the power button.

Reply to
zwsdotcom

On 15 Jan 2006 10:08:19 -0800 in sci.electronics.design, snipped-for-privacy@yahoo.com wrote,

My guess is, not easy to do what you are asking.

But, what are the numbers on that three-legged component? And what components are on the other side of that board?

If on the other side of the board is a blob of black epoxy, then forget modifying it.

Reply to
David Harmon

It may be this simple:

O button----+ +---- To circuit +-----+-- To Ckt (+) | | | | | | +------+---+ [100R] +------+ | | | | | | | | | | ----- | | | ----- | ||< | Ry2 | | N/C ----- | |NO ----- | | | o | | +-->|--+ | +-->|--+ | + | | | --- | | 1000uF --- | | | | +-------------+-------+ | Gnd

When first turned on, both relays are de-energized. The Ry1 closed point (N/C) completes the path from the O button to the circuit, which turns on. When on, the circuit provides a + voltage, which energizes Ry2. The 1000uF cap charges through the NO point. When the circuit turns off after 1 hour, the + voltage turns off. That allows Ry2 to de-energize, which closes the Ry2 N/C point, connecting the charged capacitor to Ry1, energizing it. When Ry1 energizes, it breaks the path from the O button to the circuit, putting the circuit in off mode. The cap will discharge rapidly through the relay coil, allowing the relay to de-energize. That will again complete the path from the O button to the circuit, starting the whole cycle again.

This is the hard part - finding the place on the board where + turns on when the circuit is turned on, and turns off when the circuit times out after one hour. Also, you may need to keep Ry1 energized for some minimum amount of time to allow the circuit to reset to off. That is done by increasing the resistance in the relay coil path and/or increasing the size of the cap. You could possibly go to a big super cap (1 farad, 5V) available from MPJA for $2.00 and a 5 v relay to get several minutes of delay, if that is needed.

Ed

Reply to
ehsjr

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