dig. voltmeter question

[zeeq]

I have read all old threads about voltmeters and I feel bad to bother you people with this Sorry.
I am not that expert in electronic like you guys, but I have to do something for my scool project, and I decided digital voltmeter (there are many reasons).
So I have seen schematics on the electronic labs and on the microchip for the TC7107 ( I belive thats the same like ICL7107). I dont like that one from the el.labs because I want to have a battery (maybe 9v). And I dont get something on the tc7107 scheme (someone said it is a voltmeter scheme on the page 3).
If I dont want to have lcd display, I want 4 led displays(7 segm), how should I connect it with the icl7107??
On 7107 it says 2-19, 22-25 (pin) and segmet drive to the left of the lcd, and pin 20 on the minus sign and 21 on the backplane drive. And again I am asking, how to connect the 4 led displays ?? And if I choose lcd anyway, where is that minus sign, backplane , segment??? I have one lcd and I dont kow what to conect with what?
And one more question , do I need to write a program on computer for so this one can work, or I dont have to??

Thank you very much. I know I am a newbie , but I am confused, and my teacher know less than I do, so I need help to get an A to finish my school. Well, I have time until 5th month, Please help .

https://i137.photobucket.com/albums/q220/zeeq1/ellab.gif
https://i137.photobucket.com/albums/q220/zeeq1/7107.jpg

 

[audioguru]

The LED display used with the ICL7107 uses a lot of current. If 1.888V is displayed then the current is 232mA which is much too high for a 9V battery. It needs a positive regulated 5V power supply and a low current negative supply.
The very high LED current heats the IC and affects its accuracy.

The ICL7106 operates fine with a single 9V battery because the LCD display uses a very low current.

The datasheet is confusing but shows how to connect everything. Nothing needs to be programmed.

 

[zeeq]

Thanks audioguru. I didnt know about that difference between lcd and led. It doesnt matter if I take icl7107 instead of icl7106 and connect it with lcd, or it can be only 7106 ?
And one more thing, what range can this voltmeter measure ? Its written for 200mV full scale, I dont know english so well, that means that it can measure from 0-200mV ? Is there any voltmeter that uses 9Vbatery, it has icl 7107 or 7106 and it measures for 0- maybe 30 volts (or 20V)?

 

[Nigel Goodwin]

Thanks audioguru. I didnt know about that difference between lcd and led. It doesnt matter if I take icl7107 instead of icl7106 and connect it with lcd, or it can be only 7106 ?

You MUST use the correct version IC for the display you're using - don't even think about using the wrong one!.

And one more thing, what range can this voltmeter measure ? Its written for 200mV full scale, I dont know english so well, that means that it can measure from 0-200mV ? Is there any voltmeter that uses 9Vbatery, it has icl 7107 or 7106 and it measures for 0- maybe 30 volts (or 20V)?

All meters work just like that - you simply use resistors to set the range you want, either two as an attenuator, or just one in series (which uses the input resistance of the meter as the second resistor). The datasheets for the digital meters gives all the details you need, including formulas and sample values.

 

[zeeq]

hey.
its me again... thanks guys ,you helped me a lot.

its about this sheme that one . ICL 7106.https://i103.photobucket.com/albums/m131/crazygloo/icl7106.jpg I want to set up range, maybe put 4 or 5 parallel resistors, lets say one is 10 ohm, 1kohm, 100 kohm and 1M and how much is the highest voltage I can measure with 1kohm? How can I calculate that?
Should I put these resistors instead of that one in schematic R5 (1M) or put them after R5??
Or if I cannot put the resistors I want to, how to calculate how big can they be, how many of them and what is the highest voltage each can measure??

Thanks people

 

[Russlk]

The input to the ICL7106 is open circuit, so you need two resistors in a voltage divider. You will put a fixed resistor across the input and us Ohm's Law to compute the current needed to get 200mV. The value of the resistor across the input is your choice but choose a high value. ten ohms is too low.

 

[zeeq]

Do I need for potenciometer R4 a handle?? When I am going to put that all in the box, does it (that potenciometer) must be placed on top of the box or in? Do I have to change his resistance everytime if I want to measure voltage or it is not important? I must know which one to buy, bigger one or small one...

 

[estrela]

help help help

hi!!! i was reading through the forum and just found what i was looking for... im building a digital kitchen scale for a project of mine with 4 strain gauges... to get the v out its pretty easy i used a ad620 and an op-amp for my amplifer...and also a aluminum pipe (where i put the strain gauges!)the thing is i cant get accurecy..if i put 2kg it shows +-2.5(im using multimeter to check out the outh put) ... and the other part of the project(the display) is not done yet..i have to display on lcd(and know nothing about it) dont wanna use pic to convert coz wud consume me time that i dont have now (to programme it,and i dont even know if wud work coz just have basics abou pic ),my project is due next week and in my researchs i fall in this forum where you guys are talking about icl7107 or icl7106... which lcd should i use, which converter and how should i connect it!
can i have the diagram??schematic??all components? plz plz plz....thanks in advance! ..im willing to start a new project(design from the scrash) if you have better ideas..

 

[Russlk]

I don't think aluminium is the proper material for the beam, you need something springy (modulus of elasticity you know).