Radio Temperature Sensor

I have radio operating temperature sensor. It has been working about 10 years.

The inside unit has 2 lcd which shows inside and outside temperature.
It has two AA-batteries and they last about year.

Outside unit is small box, which has two AAA-batteries.
It has gone broke and I have no idea how it operates.
I open it and it has a small chip which works as NTC-sensor dectector and then there was small amout electonics.
Well, this do not help much.

I took the electronics board out and connect external 3.0V power to it.
I started to draw citcuit diagram. The capacitors are not right, but I did't took my capacitor meter to measure right capacitors.

I started to measure voltages, but I didn't get anything.
I found that a very small circuit path didn't go through to processor.
The prosessor give the voltage to oscillator and driver circuit.

I made a small wire and solder it to both sides. Then I open my amateur radio Yeasu FT817 and tuned it to 433.92MHz and turned to FM-modulation.
Well now I can hear once an minute small humming less than 1 s.
I barely can see my voltmeter to rise at modulating input of the device.

Anyway it was now working.

I put the cicuit board back to case and put batteries on. But it don't work any more!
Jast take it out and start measuring. I can't get any voltage from batteries. The small wires from batteries to circuit board has broken.
The circuit board has been wet when I opens the device. It has been outside and there is night cold and days has 20C.
I put the device in to plastic bag and closed the mouth with the tape.

In next morning it does not work, but when the sun was shining it started to work again.
Well the wet comes inside at morning without opnening the bag.

Next thing I do, I took dehumidifier bag and put to inside the plastic bag.

Let see how it works.

Now it has been working about a month.
Now is 2019 November and it is still working
Here is the schematic diagram


Pekka OH3GDO

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