The LC Meter
SADARS Club Project
The design used is the second of two by Phil Rice VK3BHR. Full details are given on his homepage http://ironbark.bendigo.latrobe.edu.au/~rice/
The initial design together with the its conceptual origins are given at http://ironbark.bendigo.latrobe.edu.au/~rice/lc/index.html and we are using his second design with minor changes given at http://ironbark.bendigo.latrobe.edu.au/~rice/lc/index2.html
His second version was modified to become a club project for the Midland Amateur Radio Club - http://www.marc.org.au and then by G4HUP (http://g4hup.com/) who produced a kit and an article which reviewed that kit in RadCom July 2009
Our Club project will be supplied as a full kit by Richard Porter G3NII for SADARS members to construct at home using surplus two line LCD displays provided by Bryan Bourne M0BIK and some surplus resistors etc from Richard Porter. The remainder of the components and case etc are being bought in.
- A 16F628 PIC is used and will be supplied pre-programmed. It will be socketted to facilitate board testing. The full kit will be available on construction evening, 14th January 2010 or on 7th January if the parts have arrived in time.
- Software calibration is used. The finished meter can be calibrated against "any" accurate capacitor within the range 100pF to about 10000pF. A suitable capacitor (or several the same) will be available on testing evening, 18th February 2010
- A PC Board layout will be available with the kit.
There are three main changes to the VK3BHR circuit:- The 5Kohm potentiometer was found not to be necessary to set contrast on the surplus LCDs provided and has been omitted; an LP2950 is used instead of a 7805 regulator to save cost. However, there is provision for the 7805 needed if any member wishes to backlight the LCD. This will also require an additional current limiting resistor. Lastly, there is no provision for an external DC supply and its associated switch.
Special Components.
No particularly accurate components are required, except for one (or more) accurately known "external" capacitors as mentioned above, used to calibrate the meter.
- The two 1000pF capacitors are Polystyrene.
- The two 10uF capacitors in the oscillator are tantalum (for low series resistance/inductance).
- The 4MHz crystal is a genuine 4.000MHz one.
- The relay is a low current reed relay type as the PIC can only provide about 30mA of drive current.
- Don't forget the "catch" diode (IN4148) across the relay coil!
PC Board
Supplied with building and calibration instructions in the kit.
The Code
The links below take you directly to files on VK3VHB’s website.
Source code, excluding floating point +-/*
Assembled Hex code (complete, ready to work!)
Calibration Instructions.
To follow in the kit.
Acknowledgements.
The team that put this project together is comprised of (in callsign order):-
Richard Porter, G3NII; Stewart Baker, G3RXQ; Richard Giles, G4LBH and Bryan Bourne, M0BIK.
With grateful thanks to Phil Rice, VK3BHR
Richard Giles
29th November 2009
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