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9 years ago.
Interference on AD pins due to RF transmission
I am using LPC1768 for an energymeter project. I am using AD pins p15 and p17 for the current and voltage inputs. Also i am using serial tx pin p28 to transmit the data via RF (i am using a 433Mhz transmitter receiver pair) to another microcontroller which acts a a remote terminal. Now the wireless transmission is causing interference with the voltage and current signals on the AD pins. i have tried with wired serial communication using the same configuration and it works fine. So i am pretty sure the problem is RF interference on AD pins. What are the ways to reduce this interference?
1 Answer
9 years ago.
1)Pack the Mbed in a conductive box or simply in a plastic sheet for isolation and a aluminium sheet as Faraday cage.( or pack the transmitter if you have a external antenna far enough)
2) if needed a RF filter (a choke) on each wire between the Mbed and the transmitter
3)do not forget that the ADC inputs on a Mbed1768 are very noisy. Try a software filter
I have made my own radio control transmitter, with a Mbed and transmission modules 35Mhz and 2.4 Ghz. The 35 Mhz module was in a conductive box .
I monitor the battery with the internal ADC and I need a strong software filter. For the real inputs (control sticks) I use a external chip .
I dont think its noise on ADC as the readings change from like 230V to 270-290V and is constant in that range.. even the current readings go from like say 3.2A to 4.5-6A.. Another point i forgot to mention is that my mbed and transmitter module is very close to each other (on the same breadboard) and also the wires carrying the signals to the ADC are very close to the transmitter's antenna (i am using a normal single core wire as antenna). Will increasing the distance improve the results ? if so what should be the distance between transmitter and microcontroller ideally?
posted by 12 Apr 2015I have read that all ADC pins not in use should be disabled or set as outputs to further reduce noise. see: http://developer.mbed.org/users/chris/notebook/Getting-best-ADC-performance/
posted by 12 Apr 2015