Now I am checking out the 100R / 2M potentiometer dividing the NE555 based cal signal 16Hz 5V pp.
The divided down signal level should be around 5 uV * 100 / 2 = 250 uV.
I am using 3 5V source to test out.
1. 5.3V direct from 200VAC switching power supply to 5.3V DC 10A. The spikes are 80mV pp.
2. 200VAC switching power supply 12V 2A regulated using 7805. The spikes are 8 mV pp.
3. Rechargeable lead acid battery 6V * 2 = 12VDC, regulated by 7805 to 5V. The spikes are 3 mV pp.
So battery + 7805 has the smallest noise.
I have been using carbon resistors (not sure if carbon film, or carbon composite). Next step is to use metal film resistor to see if the noise gets even smaller.
.END
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