In terms of electronics, it’s what’s on the within that counts. A flowery case and person interface are good to have, however with out stable elements supporting them, they received’t be of a lot use. YouTuber GreatScott! discovered that out the laborious approach after shopping for a set of 10 thermostats to position round his residence. These thermostats are related to relays that activate valves in a boiler room to warmth the house, so accuracy is essential. However for one cause or one other, the temperature they register by no means appears to be fairly proper.
Relatively than tossing all of those in any other case slick, Wi-Fi-connected thermostats, GreatScott! cracked their circumstances open to research. The wrongdoer appeared to be an inexpensive negative-temperature-coefficient thermistor that was used to measure ambient temperature. These thermistors work by altering their degree {of electrical} resistance in response to adjustments in temperature. A circuit contained in the thermostat reads the voltage degree flowing by way of the thermistor and converts it to a temperature.
The thermistor inflicting the issues (📷: GreatScott!)
As a repair, an correct digital temperature sensing chip (WSEN-TIDS) was chosen to exchange the thermistor. With an accuracy of +/- 0.25 levels Celsius, it ought to do properly. Nonetheless, it produces digital measurements which might be learn by way of I2C, not an analog voltage just like the thermostat is anticipating.
So to get the elements speaking to 1 one other, GreatScott! designed a customized PCB for use for readout of the brand new sensor and injecting an analog voltage into the thermostat’s current circuitry. An ATtiny402 microcontroller on the board was programmed to learn temperature knowledge, then convert it right into a digital worth representing a voltage. That worth was fed right into a digital to analog converter, which produced a corresponding analog voltage. That voltage outputs to the thermostat, inflicting it to point out the right temperature on its show.
Populating a alternative circuit board (📷: GreatScott!)
Getting this all proper took quite a lot of testing and trial-and-error, as a result of the firmware supply code for the microcontroller onboard the thermostat is unavailable. However as soon as the method had been labored out, GreatScott! discovered that the temperature displayed by the thermostat lastly matched different, extra correct temperature sensors that he had available.
This may increasingly not have been probably the most direct approach to repair the issue, however given the closed nature of the {hardware}, it was an excellent resolution. The undertaking additionally serves as a reminder that generally fixing {hardware} is less complicated than you would possibly anticipate. It’s all the time value looking round contained in the case earlier than tossing {hardware} within the trash.
