Elenco Snap Circuits SnapMicro ® I Standard - Manual (Page 58)

57
PROJECT 15 – Auto Calibrating Digital Voltmeter
The Snap Circuit
® shown above uses the base-emitter junction of transistor Q2 as a reference and
calibrates the internal A to D for correct voltage readings. This self-calibration technique eliminates the
error that would occur as batteries discharge. It also eliminates A to D differences from circuit to circuit.
After building this circuit, use the flow chart and download the program shown on the next page. Open
the terminal window by pressing F8 or using the drop down under the PICAXE
® menu. Adjust the RV
slider for different voltages and press the S2 pushbutton to get a reading. When the slider is all the way
up, the voltage will equal the battery voltage.
B
C
D
E
F
2 3 4 5 6
A
G
1 7 8 9 10
To Computer
1
1
1
2
2
2
1
2
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2
1
1
1
2
2
2
2
1
1
2
2
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2
1