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Return to BlogDigital Vernier Scale Data Output Reading
Posted Jan 26, 2012 at 11:01 am
Figure 1
The project is aimed to detect the low level data and clock signal from Vernier scales with the use of the on-chip comparator in a single 12F675 PIC microcontroller.
The PIC microcontroller is connected to the Vcc and the clock & data signals from the scale through the 3K3 current limiting resistors while the red LEDs are used to limit the voltage to an approximate 1.2V. The Vernier scale body is connected to the scale’s Vcc in order to avoid short circuit from the PC ground to the Vernier body. The power from the RTS output is being stolen as well as the negative bias from the DTR output as the circuit connects to a PC communication port.
The power supply for the PIC will be limited to less than 5V by the series connection of diode and 470R resistor along with the 4V7 Zener diode. The serial output from the PIC is inverted by a universal PNP transistor while the transistor’s collector receives negative biasing from the DTR output of the PC.
Both 24-bit binary and 7-digit BCD output scale types are read by the firmware which can do fast/slow reading.
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2 years ago: when I was in high school and college, I never had the chance to see the vernier scale with digital output, only manual measurements :(