Mehmood Ahmed
New Member
I have developed a PIC16F877A MCU based circuit. that works on +24VDC input supply which is split further into 2 power supplies a +12VDC with the help of 7812 and +5VDC with the help of LM317T. I needed two reference voltages for ADC that is 1008mV and 3030mV, they are made with the help of LM317L and they are fed to opamp buffers and then from buffers to ADC reference inputs of MCU . I have used a 12VDC relay for Alarm condition which is connected to MCU port pin with the help of transistor switch and is protected with the help of free wheeler diode. Now the problem is when that relay is energized due to Alarm condition the reference voltage changes from 1012mvolts that is 4mV added to the reference the 3030mv might also change but I cannot check that because my multimeter can read up to 0~2000mV on mV volts resolution. can anyone suggest what is causing this problem?
Thanks
Thanks