- May 11, 2008
- 19,644
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Hello everybody.
On the internet several LC meter designs are available based on a free running oscillator and a gated counter. The accuracy is amazing. Claimed to be about 1 pf accurate.
The principle is pretty straight forward, but the mathematics and the translation to pic code are not. Luckily, this is already been done by Bill Carver who was the original designer if my source is correct.
I based my version on the "brazil version". Translated the words back to English and added a few instructions in the calibration section of the asm file. I also made a few modifications to the hardware to make the device more intuitive.
Now no pins have to be shorted or left open during the calibration routine.
The air coil is a home made version of about 80 to 90 windings on a plastic frame.
Be sure to use 1% 1nF styroflex capacitor for the reference capacitor. The measurement capacitor is not critical but i decided to use a 1% 1nF styroflex capacitor for this capacitor as well.
See the files section for the schematic. The pcb you have to design yourself.
Finding out how to modify the 24PF bit floating point library... Well, you have to find this out yourself as well. But it is really quite simple when using the free microchip IDE.
I used the pic kit 2 as programmer, a cheap USB based PIC programmer.
I use a 4 pole rotary switch with 3 positions for the following functions :
Off - C - L. When the device is turned on, calibration is performed automatically just as before, but now open and closed connections are also performed automatically.
The 24bit floating point FP24 math library can be obtained from the microchip website. You do have to do some modifications to the include file or you will get errors during building.
Here are a few pictures :
http://sourceforge.net/projects/improvedlcmeter/files/
P.S.
If you find any bugs, please let me know and i will correct the error as soon as possible.
On the internet several LC meter designs are available based on a free running oscillator and a gated counter. The accuracy is amazing. Claimed to be about 1 pf accurate.
The principle is pretty straight forward, but the mathematics and the translation to pic code are not. Luckily, this is already been done by Bill Carver who was the original designer if my source is correct.
I based my version on the "brazil version". Translated the words back to English and added a few instructions in the calibration section of the asm file. I also made a few modifications to the hardware to make the device more intuitive.
Now no pins have to be shorted or left open during the calibration routine.
The air coil is a home made version of about 80 to 90 windings on a plastic frame.
Be sure to use 1% 1nF styroflex capacitor for the reference capacitor. The measurement capacitor is not critical but i decided to use a 1% 1nF styroflex capacitor for this capacitor as well.
See the files section for the schematic. The pcb you have to design yourself.
Finding out how to modify the 24PF bit floating point library... Well, you have to find this out yourself as well. But it is really quite simple when using the free microchip IDE.
I used the pic kit 2 as programmer, a cheap USB based PIC programmer.
I use a 4 pole rotary switch with 3 positions for the following functions :
Off - C - L. When the device is turned on, calibration is performed automatically just as before, but now open and closed connections are also performed automatically.
The 24bit floating point FP24 math library can be obtained from the microchip website. You do have to do some modifications to the include file or you will get errors during building.
Here are a few pictures :
http://sourceforge.net/projects/improvedlcmeter/files/
P.S.
If you find any bugs, please let me know and i will correct the error as soon as possible.
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