AVR-Chat

Thank you for the reply Kat,
yes your suggestion would work well for a while but any dc component can
cause electrolysis and plating which is also accelerated by the heat of the
coolant and can eat away the electrode or the tank near the electrode fairly
quickly, the probe is usually fed with a pulse usually around 4khz through a
resistor capacitor network to remove any dc component.
The LM1830 chip also detects the resistance of the probe and turns on an
open collector transistor when the resistance increases above a preset level
(coolant loss).
I will try an avr looks like a bit of experimenting may be necessary for
reliability.
 
Thanking you.
Owen.  


-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Kathy Quinlan
Sent: Monday, 26 September 2005 9:22 PM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Water level sensing

OWEN-A 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.
> 
> Thanking you.
> Owen.    

On a car, you could use a missing pulse detector with a 556, one half to 
generate the pulse the other to detect the missing pulse, when the 
collant is up to level, it will miss pulses due to being shorted to 
ground, but when it goes low, after a short delay, the pulse is sensed 
and the output of the second half will swing, and can be used to turn on 
a led / buzzer.

Could do the same with an AVR eg Tiny15 (just remember to put a resistor 
in series with the output and sense on the radiator side of the resistor 
(470R or there about should over ride the leakage current)

Regards,

Kat.

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