Starting with version 3.7 of the alternative firmware for DPS 3003/3005/5005/5015/5020 power supplies, an optional external temperature sensor LM75 can be connected via the I2C bus. It is an affordable, low-cost, accurate digital sensor that also has an output from which a cooling fan can be controlled. This solution is relevant for DPS 3003/3005/5005 units that do not have temperature control on their board and which overheat significantly even with an average load. Although for these units, starting from version 3.6, temperature control was implemented using the temperature sensor built into the MPU-6050 gyroscope, it is nevertheless preferable to use a separate sensor on the LM75. The solution with the addition of the Lm75 sensor, even without an additional fan, allows you to protect the unit from overheating, since the output power will turn off when the temperature set in the menu settings is reached. The temperature is measured once every 10 seconds.
At startup, the firmware automatically detects the connected optional modules – the MPU-6050 gyroscope and the LM75 sensor. At the same time, on the start screen, the letters G and T are added to the version number, respectively. You can connect a gyroscope and an LM75 sensor at the same time, or one thing, or nothing at all.
The OS output of the LM75 sensor will be active (log. 1) at a temperature above 50 ° C and becomes inactive (log. 0) at a temperature below 45 ° C.
For DPS5015 / 5020 models, when the LM75 is connected, the temperature data for determining overheating and turning on the built-in fan will be taken from the LM75.
The easiest way is to connect external sensors to the U7 memory chip located next to the STM32 controller. This microcircuit has all the necessary pins – 3.3 volt power supply and an I2C bus. It should be noted that both bus wires must be pulled up to the 3.3 volt power supply with 10kΩ resistors. The SDA wire is already pulled up in the DPS board. This means that only the SCL bus needs to be pulled up. Make sure that there are no extra pull-up resistors on the SDA and SCL buses on the connected gyroscope and sensor units. You also need to remember that the OS output of the LM75 sensor is an open drain with a maximum allowable current of 10 mA.
The MPU-6050 gyroscope and the LM75 sensor can be purchased on aliexpress in the form of ready-made modules. They are also convenient because they have holes for fastening. The address pins of the microcircuit A0, A1 and A2 must be connected to GND.
For my experiments, I used an LM75 microcircuit bought in a radio store in an SO-8 package and a breadboard.
