Digital voltmeters....and more

[Miguel Lopez]

Hello everybody

I've been absent from the forum due to several reasons, but I would like to come back to share some projects that I want to begin soon. I'm in the process of gathering info to make tests and then I'll throw myself in the boiler, head first

My friend Andy (aka Diabolical Artificer) suggested me to open this thread, so here I am.

The thing is that I intend to build some measurement instruments in order to open a Metrology Laboratory to test measuring instruments from the industry. I've been a metrologist for 28 years so Metrology is a sea in which I can swim easily. I have several sensors but I lack the indicators so I think I can build them. Electricity, but also temperature, pressure, diferential pressure, and even mass. My idea is to use the ICL7135 and ICL7107 digital voltmeters for this purpose. I have the manuals of this chips and I have used (and built) the 7107 so I think this could be done.

You're all invited on this adventure


PS. The previous project, the pulse generator, was abandoned due to lack of time and electricity to work. It could be resumed in the future if I succeed with this.

[Trevor]

Welcome back I have often admired your work and posts ! So looking forward to see what you post next
Trev

[Miguel Lopez]

Thank you Trevor for your kind words. It is always a pleasure to be here.

Here the basic circuits that I intend to use. They will be a little more complex as they need zeroing and scaling, but this ones are the basic ones. As display I will use 7-seg lamps for the tests, but for the final circuits I'm also considering Nixies and fluorescent lamps (like those in the pulse generator project).

[Miguel Lopez]

These are the PCBs that I have etched to build the voltmeters. They are hand-painted and double-sided with a diferent circuit on each side

[alanworland]

Miguel great to see you, still keeping busy then! Best wishes to yourself & Yenela!

Alan

[Uncle Bulgaria]

This looks interesting! I like the style of your circuit boards - hand-drawn ones always look very appealing to me, like the organic forms seen in early PCBs before everything became rectilinear.

By 'test measuring instruments' do you mean you are planning for these to be calibration-quality pieces of equipment you can use to check factory-made instruments?

[Miguel Lopez]

Originally Posted by Alan Worland

Miguel great to see you, still keeping busy then! Best wishes to yourself & Yenela!

Hi Alan. We are all well. Our best wishes for you and Suzanne. The Selena is working as in the first day. I keep it in my bench and use it almost daily.

Originally Posted by Uncle Bulgaria

By 'test measuring instruments' do you mean you are planning for these to be calibration-quality pieces of equipment you can use to check factory-made instruments?

Yes
I have done that many times before in the enterprise where I work
The indicators are not those that provide the greatest accuracy but the sensors. I have good sensors to measure but I need to build the indicators
Are you from Bulgaria? I have some stuff from Bulgaria working everyday at home. They are from the socialist era. The motor in my bench dril is Bulgarian as well as the water pump at my Mom's. Great stuff I must say.

[mark_in_manc]

When you say 'pressure' do you mean also acoustic pressure? I have a Bruel and Kjaer 2615 microphone pre-amp (interesting one with miniature pentode valve in it) you would be welcome to have - though I am afraid I cannot spare a microphone capsule and they tend to be rather expensive!

cheers
Mark

[Uncle Bulgaria]

Originally Posted by Miguel Lopez

I have done that many times before in the enterprise where I work
The indicators are not those that provide the greatest accuracy but the sensors. I have good sensors to measure but I need to build the indicators
Are you from Bulgaria? I have some stuff from Bulgaria working everyday at home. They are from the socialist era. The motor in my bench dril is Bulgarian as well as the water pump at my Mom's. Great stuff I must say.

Fascinating! I look forward to seeing the results. Alas, while I have visited Bulgaria my only link is an appreciation of the excellent wines they're making now. The real Uncle Bulgaria is a Womble.

[Miguel Lopez]

Originally Posted by mark_in_manc

When you say 'pressure' do you mean also acoustic pressure?
Mark

Nop. Just gauge pressure, absolute pressure (perhaps) and differetial pressure

[trobbins]

Miguel, do you have resolution, voltage span, accuracy and uncertainty targets for voltage measurement for the sensors you are aiming to connect?

I have two vintage ICL7106 related pcbs, each with a different reference zener. Zener options have come a long way since the ICL710x range came out. It will be interesting to see how you go with the pcbs and if you can avoid any last digit dither.

[Gabe001]

I think you can do all sorts of interesting weather measurements with an Arduino/esp 32, and also upload measurements to an online database for remote monitoring etc. I've built an arduino temperature humidity and quality sensor with an LCD display in the past and it was quite straightforward. This is however the full extent of my knowledge on the subject, which isn't much I'm afraid.

[Miguel Lopez]

Originally Posted by trobbins

Miguel, do you have resolution, voltage span, accuracy and uncertainty targets for voltage measurement for the sensors you are aiming to connect?

Yes. I've been a metrologist for the last 28 years so, I know exactly what I need. My CMC will be low as I do not intend (nor can) to be a primary laboratory. Just to calibrate industrial equipment which are usually less accurate.

Originally Posted by trobbins

if you can avoid any last digit dither.

We'll see. I have built a couple of 7107 voltmeters (one to measure voltage and another to measure temperature) and the last digits don't "move" so much.

Originally Posted by Gabe001

I think you can do all sorts of interesting weather measurements with an Arduino/esp 32, and also upload measurements to an online database for remote monitoring etc. I've built an arduino temperature humidity and quality sensor with an LCD display in the past and it was quite straightforward. This is however the full extent of my knowledge on the subject, which isn't much I'm afraid.

Arduinos and PICs are out of the equation by several reasons. First, I have not a clue on how to use them. I would like to know but not interested at this moment because of the second reason. They are both very hard to find in Cuba, not to talk about the infrastructure needed to program them. I don't even have a laptop, just an old desk PC in our room and I don't want to transform our room in an electronics lab, so as I said, PICs and Arduinos are out of the equation, at least at this moment.

[Miguel Lopez]

Here some pictures of what I have done with the first PCB. I'm testing the 120Khz oscillator. Those test equipment are from my job, so I can say that I'm making a "foreigner" here (or in Cuban, making a goat). The oscillator chip is a CD4047.

[tritone]

Excellent, I like your circuit boards, hand made = saves a lot of time by not using software to design them. Nice projects, I will be following this thread for sure. Good luck

Muchas gracias.

[Miguel Lopez]

Here what I have done with the 7135 voltmeter. It is already working. Calibration is perfect by adjusting the reference voltage, but as trobbins anticipated the last digit has some dithering.
It moves two or three divisions while measuring. At zero it almost doesn't move, just changing the polarity signus from time to time, and maybe one division from time to time too.
I have done nothing to eliminate the dithering yet. Can you recommend me any way to minimize it?