ICL7107 Voltmeter "sensitivity"...

[madhippiescientist]

I agree!!!!

 

[lilimike]

In Post #14 qa9b is refering to this site
From this same site the author indicates these values for R3 (between pin 30 and 31) for a list of range of measurements
0 - 2 V ............ R3 = 0 ohm 1%
0 - 20 V ........... R3 = 1.2 Kohm 1%
0 - 200 V .......... R3 = 12 Kohm 1%
0 - 2000 V ......... R3 = 120 Kohm 1%

Does 0 ohm means shorting pin 30 and 31? this doesn't work in my head, does anyone have a different opinion on this?

Mike

 

[lilimike]

After looking at it long enough I figured it is probably 0.12Ω 1% (based on the other values in the range)

Mike

 

[Will_ebenezer]

replace of polarised capacitors

Anyone, do you think the capacitors in the circuit( no polarity) can be replaced with polarised capacitor?

 

[audioguru]

Electronics-Lab shows the dividers completely wrong.
Maybe Electronics-DIY copied the errors.
Why look at Maxim's datasheet when the IC was invented by Intersil?

 

[RCinFLA]

The modules with displays are so cheap it is hard to justify building your own.

(I know, the experience of building your own is priceless)

 

[KeepItSimpleStupid]

hippie:

Confucious say. He who writes long posts risks loosing them. 20/20 Hindsight say: He who posts long posts, use external program.

 

[More Coffee]

Hi All!
I'm new and a novice electrical anything . The DVM using an ICL7107 is my first actual complex circuit ..That I got to work ..thanks mostly to this thread this thing went from an uncontrolled nose dive to flying like a bird.I built it using wrong schematics and then went to Intersil and copied part for part thanks again to this thread for the Intersil noting

I differed a little from everything explained but the out come is fantastic.. I'll share a little ..

First I blew one chip up ,,I put my positive test lead on the wrong end of the 1M resistor..Learning has it price it seems.

Discouraged but not undaunted I carried on ..rebuilt the circuit still no go ..that's where this thread came in it offered avenues and idea's.
I initially built the circuit using 1" bright green segments,
For the voltage divider as mentioned low on parts and gun shy to lose another chip .I sat my divider up using a 2.2M resistor and a 100k MT Pot. set the high to 100 mv proceed to calibrate..for 2 volt to start.. That accomplished and having confidence I increased the high to 1 volt ..and adjusted the divider as needed for 0-199v.
Working well and the last digit float was minimal..
Having more confidence I messed with the clock frequency as the 100k resistor was making for slow response.
one resistor value at a time I managed to get this down step by step to 47K and from where im sitting this is acceptable..Have no idea what that is Hz wise ..my math sucks.
Re-calibrated ..and singing along ,very stable and just the odd negative segment roll just to let a guy know its running.

Next ..My 1" blue segments arrived and I pulled the green one's
Then the problems started again. Mainly display very dim. ..fearing I blew something else I put the green ones in ,perfect..Then the blue ones ..barely legible circuit went a little awry. a little research ..the blue ones are a little more aggressive than the green one's
flopping around I sat up one segment display and used NPN transistors coupled to the individual CMOS outputs, to try and pull some more current of the rail to the segment. It worked ..to well.. the transistors (BC548) seemed to latch not allowing the segment to roll with the input.
Frustrated..I began searching around for current to steal. then realised cant steal what isn't there. The circuit is powered by a 16V 1200ma wall wart..regulated by a 7805 regulator..Lots of overhead I thought The regulator was very warm ..I thought this was mainly do to the vast drop in potential,not the case ..these were to be 1amp regulators. A quick check showed a loss of 800mv with the blue leads on ..supply was cut to 4.2 volt ..with the circuit running ..These were supposed to be 1amp regulators. Rechecked every wire to find a short .nothing.
The Intersil sheet says these chip's will supply 3 volt at 8ma on 5 volt supply. Tried two more 7805's , no difference..
Took a chance and got a LM317 ..and calculated for 5.5V, I only have 5% resistor's so this would give me some head room ..All a assembled the regulator puts out 5.975V . The Max is 6V for the ICL7107. ..crunch time ..plugged in ..got a great blue display,recalibrated..and put to work ..I love this meter ...I left it for 24 hrs to soak on the bread board..it only roamed 200 millivolt on the 0-199 scale..pretty good i think..

Next I hope to use a on/on/on switch to roll the dividers to shift the scale and also the Decimal point. any ideas on this would be welcome.

Thanks to the members who assembled this thread, Its was most helpful.

 

[KeepItSimpleStupid]

Congrats: Later you'll learn about transient protection, the hard way.