[SOLVED] 7106 and 7107 functional differences re 200mV/2V scale?

[d123]

Hi!
I don't understand a difference between how the 7106 and the 7107 ADCs manage the scale and display the measured values on a 3-1/2-digit display. I have had to use a 2V scale for the 7106 to obtain the same display (is the term "resolution"?) reading I got with a 200mV calibrated 7107.

Using the same breadboard, same power supply, same circuit layout, and the exact same components, but a 7106 instead of a 7107 (and see that it needs the "jumper" from analogue common to Vin-, which the 7107 doesn't), the 7106 circuit only displayed 2 digit readings whereas the 7107 version displayed 3 digits using a 1M/10K divider.
i.e.
7107 = 1.98V/7106 = 01.9V
7107 = 5.01V/7106 = 05.0V
7107 = 8.75V/7106 = 08.7V

I changed the 7106 to the 2V full scale and now it does correctly display 3-digit readings.

I also changed the Vin+ and Vin- divider from 1M/10K150 to 10K/1K1, but I'm not so sure this has anything to do with my question as when I tested the 10:1 divider on a 200mV scale the same problem arose of the ADC not getting past a reading of approx. 2.60 on the display where it should have read 5.01. I played around with 100:1 dividers (1M/10K, 100K/1K) yesterday and the same thing kept happening with a 200mV scale calibrated to 100mV, and frankly I just don't remember if I tried a 10:1 divider then - it's all a blur of frustrated resistor swapping .

Anyway...Why does the 7106 appear to require a 2V scale but the 7107 a 200mV scale to obtain the same readout result?

Thanks.

 

[Audioguru]

The ICL7106 and ICL7107 ICs are fairly old. Maybe you are looking at the datasheet of a copycat manufacturer, not at Intersil's datasheet that shows both with a full scale of 200mV or 2.0V. Maxim make them that work better than Intersil's but the Maxim datasheet is very confusing.

 

[FvM]

7106 and 7107 have identical analog frontends, apart from a slightly different power supply configuration. Both can be used with 200 mV or 2V input range (Inhi - Inlo) by applying 100 mV or 1V reference.

 

[d123]

Hi there!
Mystery solved... Some idiot had calibrated the trimpot to 1V, and the same idiot thought it was still on 100mV

I haven't tried any Maxim stuff. The two Microchip datasheets I've needed both had a few minor mistakes (e.g. Where can I get a kW resistor, or a Farad capacitor for a tiny IC?!), but the devices themselves seem fine.

I've only used the obsolete Intersil CA3162 + CA3161 together, and the Microchip 7106 and 7107. When I looked at a couple of manufacturers' product pages for ADCs, it looks as though there is either the above type, or you have to move up to Delta/Sigma or SAR types which (from the product descriptions and datasheets I looked at) all require a PIC to interface with.

I'm a (clumsy) beginner - Is there some inbetween type of ADC which doesn't require being able to handle a PIC/microprocessor? I am under the impression that there isn't.

 

[FvM]

Your question about needing a PIC to interface an ADC isn't quite clear. Obviously, an ADC with SPI interface as exposed by most low speed devices to save pins requires a peer "talking SPI". But what's your application, where do your ADC data go?

The classical dual-slope integrator ADC with display interface like 7106 and 7107 are still manufactured, but limited in performance and function. You don't achieve better than 16 bit linearity with an integrating ADC due to capacitor loss factor, that's why they have been mostly superseded by SD ADC in slow high resolution applications.

But since the 70th when ICL710x was brought out, microprocessors have become smaller, cheaper, much more powerful and their programming is nearly everyday knowledge. No surprise that most multimeters and other simple ADC based appliances are icorporating a microprocessor respectively single chip microcontroller.

 

[d123]

Hi!

1970's circuits! - The ADC data only goes to basic circuits with 7-segment LED displays or simple LCDs; one device was a thermometer, another a voltmeter, another an ammeter I'm working on before soldering it to an SRPB, and next I'd like to learn how to make a simple milli ohmmeter using the same ammeter circuit but with a constant current source instead of the constant shunt resistor.

Thanks for your answer. I've learnt more about simple analogue devices than digital ones over the last year. I don't know what SPI is, so I'll look for an explanation on the 'net.
My programming "skills" got as far as dabbling with Visual Basic through the tutorials a few years ago (Hello World!). I'm trying to learn circuit stuff from home, so I try to take realistic steps, and think I will have problems with an SD ADC, so best go little by little.
I'm going to try an MQFP and a SOIC version of the 7106 and the 7107 respectively, mainly to continue to practice soldering tiny devices, before trying to learn how to get an SD type device or a PIC to function correctly and interact with other necessary ICs. But I know you are right, and a microprocessor is the way to go rather than 1970's "monolithic" (literally!) PDIP devices, even if they are fun to learn with.

Many thanks.