AVR-Chat

On Mon, 26 Sep 2005 21:13:29 +1000 you wrote:

>Thank you for the suggestion Ralph, the application is for the sudden loss
>of coolant from an engine, detecting the presence or absence of coolant in
>the top tank of a radiator for this the stainless steel probe works well and
>is very robust, an earlier system used a pressure switch to detect loss of
>pressure but this was not reliable.
>The pressure sensor you suggest would work but may not be able to withstand
>the vibration and heat which was the case with the pressure switch.
>I was thinking that an avr may be able to perform a simular function to the
>LM1830 by generating a pulse train on one pin and coupling this to the probe
>with a capacitor and using the inbuilt comparator. I was wondering if anyone
>had tried this.

I would be inclined to use an analog switch such an a 4053 and the ADC. Take a resistor
from Vcc to an ADC pin. Connect the control of the 4053 to a high frequency signal. The
pins ADC in and GND would connect to the switch which would reverse the output polarity at
the frequency of the control signal. The 2 output lines then connect to the water
container via small caps. The ADC pin would need a smoothing cap. thus the ADC would see
an easily measured DC value but the probe would see AC.


--
Ralph Hilton
http://www.ralphhilton.org
C-Meter: http://www.cmeter.org
FZAOINT http://www.fzaoint.net