Hello, I am trying to use a DS18b20 sensor with a STM32 Discovery board. However, I did the mistake of trying to connect the sensor to the PC using a RS232 to USB converter instead of TTL to USB. I know that the voltage levels for the normal RS232 is way higher than the 3.3-5V range of the sensor. I cant find any problems with the Simulink program that I am using, but don´t seem to get any response from the sensor. I also tried using a program from the following website: https://www.seanet.com/~karllunt/onewire_stm32f4.html The scratchpad shows only a sequence of "FF"s. Is it possible that the sensor is damaged? Is there any sure way to establish that? I would really appreciate if someone can help.
Sappy M. wrote: > I am trying to use a DS18b20 sensor with a STM32 Discovery board. > However, I did the mistake of trying to connect the sensor to the PC > using a RS232 to USB converter instead of TTL to USB. How did you do that? The DS18B20 has no matching serial interface... > Is there any sure way to establish that? Take a scope and measure whether any kind of communication happens at all. and post a schematic of your wiring.
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Ds18b20_Wiring.jpg
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Ds18b20_target.JPG
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Hello Lothar, Thank you for your reply. I used a STM32 board in between, but I was trying different things, so I am not sure whether I have already exposed the sensor to the overvoltage. I have attached a schematic of the current wiring, along with the simulink programs that I am using. The ´Target´ refers to the microcontroller and the ´Host´ to my PC. I tried with a scope to check the communication, but can´t find indication that the communication is running.
Sappy M. wrote: > I am not sure whether I have already exposed > the sensor to the overvoltage. If not shure (and not able to perform a "cross-check" with code, known as "did work previously"): assume you did kill the sensor by overvoltage. ->Buy a new one. Maybe, that is a mistake and you wastes the money for one sensor. But the effort is much less in comparision to the case you actually killed the sensor...
Sappy M. wrote: > I tried with a scope to check the communication Between what? The STM32 and the DS18b20? > but can´t find > indication that the communication is running. Is the STM32 running as expected? Then at least you should see a one-wire reset pulse on the data line..
Thanks for the replies. So I tried using the scope again. I am indeed using it in between the STM32 and DS18b20. It seems last time the time scale was too short to see that. I can see that the STM32 is running fine. It sends the reset pulse and it reads the sensor as well. But it reads only "FF"s and if I convert it to temp I get a value of 32767.5 degrees. Is this an indication of some fault? Can't find anything in the datasheet or in other forums though.
If the problem still exists, the description in the file STM32_CunbeMX_DS18B20.pdf of the appendix may help.
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