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mister-grumbler / w1209-firmware

The functional eqivalent to the original firmware of "Digital Thermostat Module Model XH-W1209".
GNU General Public License v3.0
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Hardware flaw fix #22

Open metan-ucw opened 2 years ago

metan-ucw commented 2 years ago

The board I bought worked for a while then died suddenly, upon closer inspection I found a hardware flaw in the design. The problem is that when the transistor that turns on the relay is not powered the led diode is backward biased with the difference between 12V and 5V (the power goes through the relay coil, which is just a piece of wire with hundred of ohms resistance in this case) which fries the led diode sooner or later. On the board I had the dead diode fried the AMS1117 stabilizer which passed 12V to the CPU and the CPU died as well.

Fortunately the fix is rather easy, we just need to power the led from 12V instead: W1209-fix

rtek1000 commented 1 year ago

The electronic circuit is really wrong. Thanks for sharing.

schematic