Circuit query

[johndeverill]

Hi,

I wonder if anyone can give any advice on a circuit I want to build.

I have a pressure transducer that output 0-100mV for 0-30psi.

I have a solenoid that is activated by 12v.

I want to control at which pressure the solenoid is activated.

The circuit I imagined would be the transducer sending a signal to a potentiometer and then to a transistor, which would let the 12v through to the solenoid. I thought that if I sourced a transistor that activated at 1mV the pot could be used to vary the pressure.

Does this make sense?

Also I want to put a stage in before the solenoid that would be an astable 555 circuit so that I could pulse the solenoid. Does anyone know of any example of 12v astable 555 circuits that I could use as a guide.

Many thanks in advance and hopefully someone can help!!

[ante]

Hi John,

Welcome to this forum.

I would use an op-amp for this application. What do you mean,

[johndeverill]

Hi Ante,

Many thanks for your help.

What I want the circuit to do is upon, say, 14psi being applied to the pressure transducer (46.7mV by my calculation) I want to adjust a potentiometer to vary when the transistor allows 12v to flow to the solenoid and hold it open (it is normally closed). This would be the primary circuit.

A secondary circuit would also be there, same as the first, but also with some sort of astable 555 circuit that would be activated (much in the same way as the first, I thought, with a pot/transistor) and then it would be possible to vary the Hz between say 1 and 50Hz which would then cause the solenoid to beopening and closing upto 50 times a second. I have read elsewhere that it may not actually fluctuate at high Hz but just partially open but this is fine aswell.

I have also read that it may be necessary to put a relay in line to protect the transistor.

Hopefully this makes a bit more sense of what I am doing and I do apologise for my ignorance but I am only just learning about electronics.

Thanks

John