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Saturday 4 October 2008

2nd option for one of the 1 pole 12 way switches

November 2008 issue of PW dropped on the door mat this morning.

There inside, in addition to the 2nd half of the SMT AF filter (MAX74xx chips but see later posting) P25-29 is an updated (from original design 1987 GW3JGA, JT Lawrence) LCR bridge by G4CFY, Tony Nailer.

1/2 the challange with magazine articles is finding all the components rather than buying the parts I know I have some TL072 (dual op amps) which I will employ rather than TL074 (quad op amp) and pretty sure I have other IC that are suitable to replace the Quadruple exclusive-OR gate (4070) as well as the 10K pot so going to modify the design a little. The chip count will increase but that is not a problem.

The design uses the dimming of two LED to find the NULL point.

I might see if I can improve on that as I have a null point meter, been looking for a use for it as well as a couple of small 1mA panel meters as well as a couple of PIC A/D projects using 2x40 LCD (from W8DIZ) that could be used instead.

You can use bog standard components for the range switch but I also have some multturn pots for 100, 1K, 10K, 100K and 1M so might use those to setup range values. Ditto for the capacitors. Peter at Jobdog sent me some sample SMT L which I am sure might do the job for the L as well.

I will post build pictures as I progress.

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