Hi, I read up on Velostat and decided that it could be a safe option for my task.

Now I need to find out how to switch a 1.5v dc circuit, by the change of resistance, when the Velostat is compressed.

I have a propane gas hob, that did not have a pizo ignitor. Tired of using a gas lighter I decided to investigate my options.

I bought a 1.5v dc pizo ignitor with 3 outlets. I bought 3 x pixo anodes. I installed the anodes and connected everything, all working perfect.

Now, I want to avoid installing a large push button ignitor in the furniture. I would like the ignitor to opposite when the gas tap is turned on.

I want to avoid any sparks near to a propane gas suply, so I wanted to enclose 2 strips of copper, with Velostat between them and enclosed in resin.

Now, I need to work out how to use the change in resistance to operate a relay and connect the 1.5v dc battery, to the pizo spark maker. As the Velostat does not create a direct switch operation.

Any help would be great.

 

You need to amplify the signal coming from the velostat switch.
You can use a transistor to turn on the relay.

 

You need to amplify the signal coming from the velostat switch.
You can use a transistor to turn on the relay.

View attachment 290160

Thank you Mr Chips, I was sure that it would be a transistor but my knowledge isn't sufficient.

Any suggestion to which transistor and an approximate number for the resistor that you show? I'm guessing that the diod would be a 1N4148 or similar?

 

For transistor, any general purpose NPN such as 2N3904 or 2N2222 will do.
The diode is 1N4001 series, i.e. 1N4001-1N4007.

The base resistors might look something like this setup.




R1 is the velostat resistor.

Try it first with no R2.
If the relay is always on with no R2, add R2 starting with a high resistance value.
Decrease R2 until the relay is turned off.

 

For transistor, any general purpose NPN such as 2N3904 or 2N2222 will do.
The diode is 1N4001 series, i.e. 1N4001-1N4007.

The base resistors might look something like this setup.

View attachment 290171


R1 is the velostat resistor.

Try it first with no R2.
If the relay is always on with no R2, add R2 starting with a high resistance value.
Decrease R2 until the relay is turned off.

Thanks Mr Chips, the pizo spark generator has a 1.5v battery. I also have a nearby 12v (varying) dc supply or I can run a 5v, 9v, 12v or 24v regulated voltage. I guess that I guess that I should use the 12v or the 5v, reuglated supply, for the resistive switch, to operate the relay and complete the circuit for the spark generator. Do you agree? If so, what voltage relay do you think would suit this situation better?

 

You choose the relay and supply voltage together to match.
You can use a supply voltage higher than the relay by inserting a resistor in series to reduce the voltage to the relay (i.e. limit the current through the relay).

In either case, regulated or unregulated supply should not be too critical.