View Full Version : More info on L4620 liquid sensor chip

- 13th August 2007, 18:48
Hi all,

Few days ago I ran across an interesting liquid level switch IC made by ST Microelectronics. The part # is L4620. This is a 8 pin dip device which, according to the specs, can safely detect the presence or absence of a liquid between two electrodes.
It also has few nice configuration options, built in delay and alarm latch.
I found it at All Electronics, the electronics surplus distributor.
They also provide a link to a data sheet (http://www.allelectronics.com/spec/L4620.pdf). Unfortunately the data sheet is a bit unclear on the RC network associated with the sensor (Ra, Rb, Rc, Ca, Cb, Cc).
I Google it but I was unable to find any more information. What is strange is even ST Microelectronics site does not give any hits on the device made by them.
Trying to call the few places listed on the site did not help, not to mention that one phone # is disconnected.

So, my problem is finding some more info on how to design the sensor RC network to get the chip going.

Did anyone use this chip or does anyone have more info on how to use it?
It looks like a pretty good chip for only $0.50 in low quantities and it can make a really small, reliable, sealed sensor for all kind of home or automotive applications.

Any info in this matter will be greatly appreciated.

Best Regards,


- 14th October 2007, 05:45
Quite frankly, the ST-L4620 looks like a dud to me. The output is fixed frequency (Fosc/32) and you have to make a judgment about the amplitude and wave shape to decide the liquid present/absent. That takes an ADC plus some arbitrary algorithm that you need to develop for yourself.

For less external parts than needed for the ST-L4620, you can use a 555 timer and monitor the pulse width of the output. The timer MUST be a CMOS 555 variant and not the bipolar type. The frequency varies enormously with moisture present/absent so the whole system is digital, needs no ADC, and can be set with good confidence that your pulse width decision points will be right first time.

Take a look at


You can drop off the voltage regulator and drive the whole system from the processor supply voltage, I have used this system for moisture sensors and it is extremely sensitive to (water) moisture. Not sure how it goes with non-polar solvents but that is not covered for the ST-L4620 either.


- 16th October 2007, 01:30
Hi Brian,

Thanks for your input.
The main reason I was trying to use this chip is that with only a few external components you can safely detect if the level gasoline is under a certain level.
If I got the specs correctly the chip will do all the work if you use a capacitive sensor.
For fuel level detection in my case Iím limited by the size of the sensor and Iím not allowed to change any of the inner components.
Iím working on a similar sensor to the one presented on the site you suggested.
Due to very small change in capacitance from the sensor Iím targeting higher frequencies. So my tests show that a 14 stage binary counter with built in oscillator (MM74HC4060) might just do the job.
I will need a small PIC to process the output of the divided down frequency.
Unfortunately I didnít have the chance to work on this project lately, so I donít have too much progress to report.
I will post my findings as soon as I will have news.

Best Regards to all PIC users,


- 30th May 2008, 02:08

I'm an electrical "newbie", but your post gave me some good ideas. I have a digital peristaltic pump which will turn on when the resistance on an input jack RISES to a certain point. Naturally a dead short will turn it off, but the "turn on" point can be adjusted. I'd LOVE, LOVE to use this pump to water plants when they need watering, and can envision a high-hanging pot with two stainless probes on opposite sides of the pot determining the need to water ( or not). The two probes would output a resistance that, when low enough, would cause the pump to turn off and stop watering. Then, when the plant dries to the point when it needs water, the pump would turn on.

How can I create a circuit using a 555 chip that will do this??

Hopefully, thanks in advance

Stan F.

- 1st June 2008, 23:03
Take a look at