Hi Eric,wlpThis circuit is a low side current measurement of a motor using a shunt resistor and adc of a mcu. However, I do not understand the reason or use for the 100k internal pull down resistor, 10k external serial resistor and the capacitor. Anyone can help?
View attachment 297718
Thanks!!Hi,
Vshunt= 2.74R * 0.02A= 0.0548V
Vadc = 100k/(100k+10k)= 0.909
0.0548V* 0.909 = 0.0498V
0.0498v/3.3v= 0.015 * 4096 = 61 Counts.
E
The choice of resistances is based on assumptions about both the actual motor current and the input voltage range of the ADC.wlpThis circuit is a low side current measurement of a motor using a shunt resistor and adc of a mcu. However, I do not understand the reason or use for the 100k internal pull down resistor, 10k external serial resistor and the capacitor. Anyone can help?
View attachment 297718
Hi Bill,Thanks. The motor is driven by 5v. Based on 12bit ADC, Vref = 3.3v, for a 20mA current through the shunt resistor, am I right that the ADC count is 61?
It is unlikely that the resistors in the divider are exactly those values. even 1% tolerance (precision) resistors allow variations.Hi Bill,
There are no assumptions about the motor, or the circuitry, the figures posted were clear and concise.
Rsh=2.74R, Motor Current 20mA, 10k/100k resistive divider, 3.3Vref, ADC 12Bit.
I am at a loss regarding the point/purpose of your post that raises doubts regarding such clear-cut values.??
E
E.G. is certainly welcome to ignore what say. However, for data, resolution not stated is usually not implied. 20 Ma is not the same as 20.00 mA, and 2.74 Ohms is not likely quite the same as 2.7400 ohms. Using a voltage divider will certainly reduce the resolution of a reading on an A/D converter.Hi Bill,
Forgive me for being blunt, but you are talking nonsense.
E
In that case, what were your reasons for commenting on the lack of information on voltage and current?Hi Ian,
The TS did ask for our opinion of his circuit, just a request for confirmation of his result of 61 counts in an ADC buffer, using the circuit parameters he posted.
E
You have not stated the motor voltages or currents.
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