Barnstorming in my underwear, a DIY story

[banned]

i'm not very active, but i do often take advice anyway... we'll see

it was an exploratory question. what's up next?

[NoiseWiki]

Forest Mims books are a good place to start.. back in the day if you hung out at Ratshack this was your goto

https://www.noisewiki.com/files/Getting ... M.Mims.pdf

[FAP]

Is this still a xe2x80x9cask crochambeauxe2x80x9d thread? Ixe2x80x99m confused.

[NoiseWiki]

Is this still a xe2x80x9cask crochambeauxe2x80x9d thread? Ixe2x80x99m confused.

It pretty much got derailed by a bunch of frivolous questions but I'm sure if you ask an actual practical DIY question he will try to answer it.

[crochambeau]

Is this still a xe2x80x9cask crochambeauxe2x80x9d thread? Ixe2x80x99m confused.

I'll answer inquiries, but welcome other answering entities as well.

After digesting it a minute (and observing the trajectory defined by early onset erosion, er, questions) I decided a just me framed thread was a terrible idea.

[NoiseWiki]

decided a just me framed thread was a terrible idea.

You meant well.

[FAP]

Ok, so I know there's a way to continuously activate those circular pressure(?) pads found in some electronic toys. Like these ones:

61XJy+43cfL._AC_.jpg

I know I asked this question before, and it involved using a transistor soldered in some way between the two sides of a given pad. I tried it but never got it to work, so my questions are,
1. is there a way to trigger these pads so that they run continuously, preferably without having to draw current from a separate battery? and
2. is there a way to do this with a 555 chip?

[crochambeau]

Ok, so I know there's a way to continuously activate those circular pressure(?) pads found in some electronic toys. Like these ones:
61XJy+43cfL._AC_.jpg
I know I asked this question before, and it involved using a transistor soldered in some way between the two sides of a given pad. I tried it but never got it to work, so my questions are,
1. is there a way to trigger these pads so that they run continuously, preferably without having to draw current from a separate battery? and
2. is there a way to do this with a 555 chip?

Your image file is not coming through, but usually a pressure pad is going to be a switch. Am I on the right track?

If those switches are interfacing with digital circuitry they typically toggle from one state (high or low) to the other, if this is the case sticking a 555 in its place should work fine. All a 555 does at the output is alternate opening and closing two transistor switches, one referencing "low/ground/Vee" and the other referencing "high/power/Vcc".

What you need to do is measure the pad under operation.

Record a measurement of the pad in the idle state, and record a measurement of the pad in the pressed state. If there are other pressure related states, record those too, but understand it has probably left the domain of a 555 if you need to recreate the middle ground.

Now you should have a representation of the switch. I'm guessing it's an on/off sort of thing and there's a voltage of some sort involved.

Recreating that is easy to do with a 555 if the on/off amounts to "very close to your power rail/very close to ground", just sort your timing needs via standard circuitry and connect the output of the 555 directly to the "input" side of the switch (ie: one of those pads carries the DATA and the other carries the REFERENCE, ignore the reference as it is now supplied by the 555, it is the data line you need to tap).

Another possible circumstance is that the switch is supplied by an intermediate voltage that is supplied by the circuitry it is supporting, it is inadvisable to introduce the power rail as information if the switch is on something like a 3.3 volt leg. In this instance you either plant a switching transistor (I'd grab a mosfet) in place of the switch (sounds like what you've tried in the past to less than stellar results?) and maybe drive the gate of the mosfet with the 555 which will in essence decouple the power rail from the information rail.

There are more potential layers, like a switch matrix, but we're talking about a kids toy and I'd expect little resistance to learning its secrets.

The crux is: you've got to measure out the system you're working on to tailor the best solution.

I might be more help seeing the image, but I might not. Getting voltage measurements of the various states is FAR more valuable than looking at a colorful plastic circle.

[FAP]

Got it:

Viewed 1983 times

EDIT specifically this part:

Viewed 1982 times

[crochambeau]

In this example - using this particular part, you can visibly SEE the pad connection to ground plane (plane itself poured in the color green here).

Viewed 1981 times

So, with respect to that particular pad, we need to understand what states are available in use at the circuitry end (in black).

If you're connecting this to original equipment, you need to find out (typically through direct measurement and observation) what states are expected at the switch.

We can surmise that the switch connects to ground/low when pressed, so it boils down to what "high" state is at that pad. If it is connected to a microcontroller with a pull-up resistor to the Vcc/positive power supply, then you can get away with connecting a 555 directly. If it is a "supplied" logic line, that is to say completely internal to the logic chip without an external power supply reference, you want to AVOID putting power on it (which would happen minus transistor loss with a 555 directly connected) by using the aforementioned transistor/mosfet switch as a sort of buffer.

There are also instances where neither side of those connection pads are fed to a common plane, in those instances I would also advise against a directly connected 555 because BOTH or EITHER voltage reference can be damaging. Those too would require a buffer.

Viewed 1981 times

In the above "HIGH" is whatever high reference (the higher voltage measured, typically), and "LOW" is the return or, in the case of the controller PCB you supplied, ground. GND is ground from the 555 timers point of view, not necessarily the same thing as reference LOW on the switch. The resistor can be any moderately high value, say over 10K and is just there to provide a path to ground for stability. I think it can be argued that you can sink or source through the 555 itself and that completion path (offered by the resistor) is unnecessary, but it's common practice. That said, don't plant a pull down resistor (that is what R is in the diagram I provided) when there is already a pull-up resistor, or you'll confuse the states (high and low).

If I were building this I'd grab a 2N7000 for the switching MOSFET, but only because I have a supply on hand. You can get away with MANY different parts, but unless you are working that switch into a known GROUND on the low side, I would avoid using a BJT due to introducing current path through the base.