6 Replies Latest reply on May 13, 2019 9:30 PM by VasanthR_91

    TMP05 limit count > 4?


      Is there a reason - besides conversion time - to limit the maximum number of TMP05 sensors in the chain to 4 or less? could it be like 16? I know the conversion time increases dramatically, but I am trying to scan at least 12 sensors and control 2 fans with them... (highest out of 6 would determine the speed of each fan...)

        • 1. Re: TMP05 limit count > 4?



          Can you try using the multiple instances of the same component(with 3 different daisy chains). As the component has the max limit of 4 sensors in the chain, this may be help in measure 12 sensors.

          • 2. Re: TMP05 limit count > 4?


            For large number of temperature sensors you may consider DS18B20 digital sensor

            Component to read DS18B20 digital temperature sensors


            The associated component offers 8 sensors to be simultaneously sampled. Using two components will provide 16 sensors. (A single component can be upgraded to sample up to 32 sensors simultaneously without loss of performance - let me know if this option is required). The sensor is about same price as TMP05 ($3.06 vs $2.21), but need no PCB for mounting. The absolute temperature accuracy is 0.06C - much better than 0.5C for TMP05. Temperature conversion is performed at each node internally, so no hardware resources are needed on PSoC side.


            • 3. Re: TMP05 limit count > 4?

              While the price of the TMP05 is $2.21 in single units, its $0.72 in multiple. The DS18B20 (now DS18S20) has one serious problem and that is that its a PITA to determine the LOCATION of a specific sensor. While One Wire Sensors are easy to use, you'd have to create a dictionary of which sensor is where..


              Another sensor - which has a great single unit price is the MCP9700, which somes in a TO92 format. It does require an ADC on the backend, but is very palatable in price: $0.26 in single quantities at digikey.

              • 4. Re: TMP05 limit count > 4?


                DS18B20 is now "DS18B20+" (12-bit). The DS18S20 is 9-bit counterpart.

                TMP05 needs some PCB for mounting, which negates price difference.

                Some node location assignment required in any case, unless all sensors go along some pipeline.


                • 5. Re: TMP05 limit count > 4?

                  The TMP05 sensors are positional. That means that one can daisychain a number of sensors and then read them, but the sequence doesn't change. The first on the chain is #1, etc.

                  DS18B20+ sensors are not, code would have to be taught one sensor at a time to determine it's location...

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                  • 6. Re: TMP05 limit count > 4?

                    Hello Maurice,


                    The limitation comes from the DiscoverSensors API, and it waiting time (counter resolution) for the more than 4 sensors discovering.  You may not be able to use more than 4 sensors with one component. You may either use alternative sensors suggested or multiple components(as long as enough UDB resources are available in your device).

                    Best Regards,