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Old 15th Apr 2017, 12:06 pm   #1
GeoffK
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Default D.C. Volt Meter

Forgot I made this quite a while ago from a Radio Constructor project (March 1972), powered it up with two PP3's and it still works and is accurate enough to test circuits. It uses the LM709 Op Amp and has a 10x gain with 100K Ohms input impedance. I only fitted resistors for ranges from 100mV to 10Volts as I couldn't afford the larger value resistors at the time for the 30, 50, and 100Volt ranges. I laid it out differently to the original Radio Constructor design with the controls such as Set Zero and meter 'Off protect' switch combined with the on/off switch at the front. The meter only has rough pen markings on but is good enough for home use. The front panel was sprayed with Hammerite and clear varnish that has lasted quite well.
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Old 15th Apr 2017, 9:09 pm   #2
ionburn
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Default Re: D.C. Volt Meter

Nicely constructed
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Old 15th Apr 2017, 10:05 pm   #3
ParcGwyn
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Default Re: D.C. Volt Meter

Nicely made, I always like to see homemade test equipment.

Dave

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Old 15th Apr 2017, 11:38 pm   #4
Peter.N.
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Default Re: D.C. Volt Meter

Very neat, somewhat above my standard of construction.

Peter
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Old 16th Apr 2017, 10:15 am   #5
GeoffK
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Default Re: D.C. Volt Meter

Thanks for all your comments, it seemed more fun back then to buy components from places like Home Radio and Henrys without to much regard of it being uneconomic to make. The yellow switch wiring is a bit untidy as I thought I might get round to fitting the remaining resistors.
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Old 17th Apr 2017, 6:22 pm   #6
MrBungle
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Default Re: D.C. Volt Meter

I like the hammer finish. I come from a family that applied Hammerite to literally everything so I have fond memories

Good point with the economics of building versus buying stuff. I recently built a FET voltmeter myself. Yes you can get a perfectly good DMM for £2.68 on CPC and my "main" Fluke, an 8021B, cost me £21. I must have spent twice that building a technically inferior voltmeter. However, I learned a lot more building something than buying and enjoyed the process immensely and that is priceless.

It's still more fun to build versus buy.
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Old 18th Apr 2017, 9:42 am   #7
GeoffK
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Default Re: D.C. Volt Meter

This is the circuit of the D.C. Voltmeter. I agree about the Hammerite it is a very good paint.
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