Hey everyone. I have not been posting much lately but tonight I did a little mod that I thought I would share.
I have two of these 1F78 non-programmable thermostats laying around since I replaced them in my house. I couldn't help but notice that the insides of these seem to indicate that they could possibly be made programmable somehow.
Tonight I started looking at this board for clues as to what it was missing. There were a few missing resistors, a missing LED & transistor under the display as well. I starting googling for the model number and found a picture (last attached picture) of the programmable model. So I studied it closely and determined the differences.
A short time later I un-soldered the zero ohm resistor from W1, soldered a jumper on W2, soldered a jumper across W903, and added a missing 1000 ohm resistor at R10 to connect rest of the button pads to the CPU. I put the batteries back in and my non-programmable thermostat is now programmable! Look at the last picture for programming instructions.
The only minor caveats are the lack of button holes on the cover and the hole for the display is cropping some of the LCD. But since I am just going to use this as a thermometer, it is nice to have a clock along with it.
It makes sense from a manufacturing standpoint to have one circuit board that can be both programmable and non-programmable with only some trivial modification. And then they slap on a different cover with some extra button holes. Lo and behold, they can now charge 50% more for the same basic unit.
I have two of these 1F78 non-programmable thermostats laying around since I replaced them in my house. I couldn't help but notice that the insides of these seem to indicate that they could possibly be made programmable somehow.
Tonight I started looking at this board for clues as to what it was missing. There were a few missing resistors, a missing LED & transistor under the display as well. I starting googling for the model number and found a picture (last attached picture) of the programmable model. So I studied it closely and determined the differences.
A short time later I un-soldered the zero ohm resistor from W1, soldered a jumper on W2, soldered a jumper across W903, and added a missing 1000 ohm resistor at R10 to connect rest of the button pads to the CPU. I put the batteries back in and my non-programmable thermostat is now programmable! Look at the last picture for programming instructions.
The only minor caveats are the lack of button holes on the cover and the hole for the display is cropping some of the LCD. But since I am just going to use this as a thermometer, it is nice to have a clock along with it.
It makes sense from a manufacturing standpoint to have one circuit board that can be both programmable and non-programmable with only some trivial modification. And then they slap on a different cover with some extra button holes. Lo and behold, they can now charge 50% more for the same basic unit.
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