Inductance
and
capacitance
adapters for a digital voltmeter
The
adapters have been built from the drawings in chapter 26 of the ARRL
handbook
for radio amateurs, 2000 using the ARRL PCB
templates.
They convert capacitance/inductance to mV to read on a digital
voltmeter:
Capacitance is in two ranges: 2.2-1000 pF or 1 – 2200 nF, and
inductance
in these two ranges: 3-500 uH and 0.1-7 mH.
The
projects can be found here.
Errata for the
capacitance
adapter:
- The PCB
template is
incorrect. There is a connection between pin 7 of U1 (ground) and the
minus connection of the DVM that needs to be cut away. In the template,
the trace from pin 7 going down for a few mm and then to the right
should only go to the next hole where the strap is soldered. Then it
should be cut, and not be allowed to connect to the junction of the
parallel capacitors C5 and C7 (whose sum make up 0.2 uF).
Recommendation
for the inductance adapter:
- There are
sharp pulses
in the supply voltage unless a couple of decoupling capacitors are
added as in the capacitance adapter. The values are not critical, e.
g.: 10 uF/10V on the 9V supply, and 1.5 uF/10 V on the 5V supply.
22 Apr 2003.
LA3ZA, Sverre
Holm