Electronic "soft" button bypass

[LouF]

The Star Shower Motion laser decoration light has a motion button that toggles the motion on and off. Upon shutting off the power (either by switch or timer) its motion needs to be manually started. It appears to be a soft-switch, and I was thinking of trying to bypass it with, possibly, a capacitor. My thought is that upon power-up, current could flow simulating a manual push, and as it is charged the current flow would be impeded; I don't think a hard-switch would be the way to go. Any thoughts?

 

[dknguyen]

I'd just hard-switch it to be honest...through a 1K resistor or something like that if you're uncertain. Unless there's a reason it cannot be hard-switched (i.e. maybe it detects an edge rather than a level after it has finished starting up).

 

[gophert]

The Star Shower Motion laser decoration light has a motion button that toggles the motion on and off. Upon shutting off the power (either by switch or timer) its motion needs to be manually started. It appears to be a soft-switch, and I was thinking of trying to bypass it with, possibly, a capacitor. My thought is that upon power-up, current could flow simulating a manual push, and as it is charged the current flow would be impeded; I don't think a hard-switch would be the way to go. Any thoughts?

First measure what the voltages are on each side of the switch (not pressed) then measure again when pressed. Keep negative (black) lead on circuit ground and measure the voltage at each pin of the switch with red probe. If one is equal to ground, measure resistance from that lead to ground (likely 10k). One will likely be equal to circuit supply voltage (5v?). Then we can start talking about your options.

 

[LouF]

I will try. Be back in several days (Sun.-Mon.).

 

[LouF]

I have a 1/2W R ready and am tempted to permanently add that, but I don't want to burn it up (of course). I will need several days to get to it. Thank you.

 

[JonSea]

Try it with clip leads first. The circuit may not work with the switch bridged out. It shouldn't be harmed - it just may not work as you hope.

 

[LouF]

Will do. I thought I had a better assortment, but my closest pick is 16V47uF

 

[LouF]

I'd just hard-switch it to be honest...through a 1K resistor or something like that if you're uncertain. Unless there's a reason it cannot be hard-switched (i.e. maybe it detects an edge rather than a level after it has finished starting up).

That isn't working. It needs a change. Shorting (jumping) the contacts will still toggle on/off.

 

[dknguyen]

oh, I understand your first post now. Did not fully register. It's a momentary toggle. I assume it also only takes action on release? Or does it take action on press? What happens if you just hold the button?

Do you have a dmm to do gophert's tests?

 

[LouF]

First measure what the voltages are on each side of the switch (not pressed) then measure again when pressed. Keep negative (black) lead on circuit ground and measure the voltage at each pin of the switch with red probe. If one is equal to ground, measure resistance from that lead to ground (likely 10k). One will likely be equal to circuit supply voltage (5v?). Then we can start talking about your options.

The switch sees ~2.8VDC, the other side of the switch is 0V. While holding the switch, each was 0V. The resistance from the "GND" side is 0 ohms. I measured to a strip that appeared to be GND as a guess - I'm assuming that is right. The positive voltage seems to come FROM an IC chip; the other side goes to somewhere I can't follow.

Shorting the contacts (on the PC board) toggles on/off (as expected, lol), jumpering the contacts does not result in desired motion-on-power function. I tried capacitors (47uF 16V and 1uF 50V, separately), and it did not work. Plus, I forgot that they will hold the charge. Shorting the contacts with a capacitor in place still toggled on/off motion.

Attached are photos with text annotations for clarity.

 

[LouF]

oh, I understand your first post now. Did not fully register. It's a momentary toggle. I assume it also only takes action on release? Or does it take action on press? What happens if you just hold the button?

Do you have a dmm to do gophert's tests?

Hello dknguyen,

It appears to be a bubble-contact type switch (feels, sounds). It will conduct while depressed. Pressing of the switch toggles on/off this device's "motion" (a motor that provides kaleidoscope-type action) ; continued depression acts as one press, and it does not seem to damage the circuit or change function while being continually pressed. Action happens at first press, not on release.

Yes, I have multimeters, and I took the readings.

 

[dknguyen]

From the measurements, even though you weren't able to follow the board to get one of them to really confirm things, it seems like a pull-up input where the button pulls the input down when pressed. That measurement is measuring the resistance when the unit is unpowered between the 2.8V side of the switch and the regulated power supply (which should be 2.8V or somewhere around there...probably 3.3V). But you seem to be unable to find it. You might be able to find it by measuring the pins around the most prominent ICs relative to ground and see what the highest voltage encountered is. What you really want is the regulator which might be that IC with the 4 pins (one large one on the left, and three small ones on the right) to the bottom left of the central IC.

It might be debouncing or detecting the edge sometime after power up which would make the hardshort not work because otherwise a hard short should do the job for a pull-up circuit. If the unit is unpowered, and you hold the button while powering it up, I assume it does not react at all? That should be the same thing a hard short across the switch.

So if it was looking for an edge, placing a capacitor across the switch should do the trick. Holding the charge isn't a big issue since you can always put a high resistance (100k) value across the capacitor as well which will slowly drain it empty when unpowered. But if the circuit still isn't reacting to that, then it could be that the rising edge that it is looking for is too slow. Hmmm.

 

[LouF]

From the measurements, even though you weren't able to follow the board to get one of them to really confirm things, it seems like a pull-up input where the button pulls the input down when pressed. That measurement is measuring the resistance when the unit is unpowered between the 2.8V side of the switch and the regulated power supply (which should be 2.8V or somewhere around there...probably 3.3V). But you seem to be unable to find it. You might be able to find it by measuring the pins around the most prominent ICs relative to ground and see what the highest voltage encountered is. What you really want is the regulator which might be that IC with the 4 pins (one large one on the left, and three small ones on the right) to the bottom left of the central IC.

It might be debouncing or detecting the edge sometime after power up which would make the hardshort not work because otherwise a hard short should do the job for a pull-up circuit. If the unit is unpowered, and you hold the button while powering it up, I assume it does not react at all? That should be the same thing a hard short across the switch.

So if it was looking for an edge, placing a capacitor across the switch should do the trick. Holding the charge isn't a big issue since you can always put a high resistance (100k) value across the capacitor as well which will slowly drain it empty when unpowered. But if the circuit still isn't reacting to that, then it could be that the rising edge that it is looking for is too slow. Hmmm.

I'm sure I didn't get this as you were asking, but I measured the resistance between the 2.8V side of the switch and the 5V positive power supply lead (while unpowered) as open-circuit.

Correct, the motion button has no effect while pressed upon power-up.

Is it possible an inductor should be used to close the circuit?

I added labels to items I believe to be ICs (U1-U5, in yellow).

 

[LouF]

... if the circuit still isn't reacting to that, then it could be that the rising edge that it is looking for is too slow. Hmmm.

I have it working, but I haven't found a consistent time to use, especially from a dead start-up.
I'm using 100uF cap. and I'm estimating a 63k resistance. 6>t>2 seconds works at times.