Auto Turn ON and OFF

[Otchu]

Hello everybody

I need to develop a ohmmeter with a auto power ON/OFF when I do apply a resistance(between 0ohm and 2ko) on the circuit ... My problem is how can I do that ? I need to detect the continuity to turn ON the circuit (I gonna use a PIC 12F615) but can not modify the signal to be able to use it on the analog input of the PIC


Thank you very much for the help

 

[MacGyverS2000]

These fora are for practicing engineers, not students/hobbyists.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Otchu]

Sorry but I am engineer !! I am doing FPGA design and the question I am asking is about analog electronic ... something I don't have a real skill for it

 

[OperaHouse]

Define what you consider ON/OFF. A simple current sense could take the micro out of a sleep mode and/or turn on and off a display. Something would always have to be "on" with some voltage applied to sense a resistance has been connected.

 

[Otchu]

The problem is the current can not be more than 1.3mA on the resistor (the resistor is actually an explosif (I am working in blasting machine business)). So trying to have a good reading on the resistance and using this signal to turn OFF the uP is not really easy to figure out ! I was wondering if somebody knows a specific chip who can do this kind of job

 

[Skogsgurra]

Let one pin output a high signal through a 100 kohm resistor. Let the AD input be a HiZ digital input pin. No current will be drawn.

When a low ohm circuit is connected, the voltage drops below 1.5 V (probable threshold for the input pin). Once that condition has been detected, shut off the output pin and start measuring. When measured resistance gets above your measurement range, just go back to state 1.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[MacGyverS2000]

Not to put too fine a point on it, but what is an EE doing working on a project using explosive triggers when he doesn't have the experience to do so? Seems like a recipe for disaster. Even if you take what we give you here and implement it, what's to say what we tell you is exactly right for the project at hand (which we cannot see)? Someone is bound to get hurt/killed.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

...the current can not be more than 1.3mA on the resistor (the resistor is actually an explosif (I am working in blasting machine business)).

This has "intrinsically safe" written all over it.

It's not exactly the same as that applied for use in potentially explosive atmospheres, but it's along the same lines.