- Voltage follower on PA6 & PA7 for bias buffer (note: HAL_OPAMP_Start(&hopamp2); required)
- Implements @Robert.Wall's offset removal technique
- Extension of the 1CT example to 3 CT inputs.
Anti-alias filter based on:
Two 1k resistors + 22pF capacitors to ground, biased with output from voltage follower.
40W incandescent lightbulb:
Vrms Irms RP AP PF Count
239.86 0.184 43.8 44.1 0.995 287122
239.85 0.183 43.8 43.9 0.998 289544
239.94 0.184 43.9 44.1 0.995 289507
240.07 0.183 43.9 43.9 0.999 287142
240.12 0.184 43.9 44.1 0.996 289462
239.98 0.184 43.9 44.1 0.995 282377
239.76 0.184 43.8 44.0 0.995 284698
Electric room heater:
229.96 7.908 1816.4 1818.5 0.999 289401
229.84 7.901 1813.9 1816.0 0.999 291787
229.83 7.900 1813.5 1815.6 0.999 289468
230.05 7.907 1816.9 1819.0 0.999 289500
230.07 7.907 1817.2 1819.2 0.999 287145
230.05 7.906 1816.7 1818.8 0.999 291873
Laptop:
239.41 0.134 17.1 32.0 0.535 287153
239.48 0.139 17.9 33.2 0.540 284790
239.58 0.140 18.1 33.4 0.542 291839
239.62 0.144 18.8 34.5 0.544 287131
239.50 0.132 17.0 31.6 0.538 289426
239.45 0.136 17.6 32.5 0.541 291730
Readings are printed every ~2.5 seconds (125 cycles 50Hz), ~287122 VI sample pairs every 2.5s = 115 kHz
22pF filter cap on CT input:
100nF filter cap on CT input:
No filter cap on CT input:
100nF filter cap on Voltage input (22pF on other screenshots), showing to low cut off frequency:
