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  1. I fixed it using this datasheet : http://www.datasheetcatalog.org/datasheet/TelComSemiconductor/mXrtrqt.pdf I used the top right schematic on page 19. The only thing i added was a trimmer over pin 30 and 31 so i could finetune the voltmeter. Now it works perfectly, it's on par with my DMM. I'll post some pictures tomorrow when i got some time. Next thing i need to fix is the shunt for my ampere meter. Does it need an extra galvanicly seperated power supply next to the one of my voltmeter? Or can i use the same? I also put some knobs on the potmeters, but i think i broke one of them by using too much force. When i turn it it goes to 21.1V when i turn further it goes back to 15V. Before it regulated to 31V. I'll look into it later. I'm glad my voltmeter works finaly.
  2. I noticed that too, but on this site they say you can adjust the scale with a resistor between pin 30 and 31. That's why i used a 12k resistor for 0-200V. edit: so i took out the fixed resistor between pin 30 and 31 and switched it with a trimmer. Turns out it needed to be 31,5k. Strange but i knew something was wrong with the resistor/capacitor combo. Thanks for your time and help. I still have one more question though. I have a second meter wich i use as an ampere meter. But does it need and extra power supply different than the one supplying the voltmeter? Now i have a transistor that goes to a 30Vdc power supply and to another transistor. That transistor goes to a 5V and -5V power supply. Can i use that supply to power both meters? Thanks in advance. edit: This is getting really frustrating. I'm getting a feeling this icl7107 chip is crap. First when the multimeter was supplied by my 30vdc variable power supply it measured the 1,58V battery perfectly. Now with the icl7107 voltmeter in the 30vdc power supply it shows 3V when i regulate from 0 to 3V. The leds don't go beneath 3V for some reason. It's so weird. I did the trimmer back to 11k so the voltage division is set for 0-200v. I connected pin 32 to GND as recommended by this guy http://www.electro-tech-online.com/electronic-projects-design-ideas-reviews/109313-icl7107-voltmeter-sensitivity-2.html#post897696 I removed the 47k resistor and put back the 470k resistor for 2V full scale. Still didn't work. So tomorrow i'm going to put a 10k trimmer instead of a 2k trimmer to regulate the reference voltage. I couldn't get it higher than 315mV and it needs to be 1V. If that doesn't work i'm going to switch the cap at pin 27 for a bigger one (1
  3. Did some new tests. I replaced the 12k resistor between pin 30 and 31 with a 10k resistor. Now i get weird results. So i leave the measuring points unconnected (floating). With the 12k resistor i had 00.0V but with the 10k resistor it rises to 38.xV. Then i measure the 1,58V battery and it shows 34.xV. Then i switch the polarity and it shows -20.XV. When i unconnect the measuring points and leave them floating the -20.xV slowly decreases. I'm guessing my capacitor/resistor combination is faulty. I'm using a 103 (10n) ceramic disc capacitor and a 10k(9,98) resistor at the moment.
  4. I'm going to put in the 1k trimmer this evening (if i have one). that is the only thing that still differs from the datasheet. This is how i use the voltmeter : In my 30V dc power supply i have a circuit with a 5V voltage regulator that is connected to a transformer. That transformer is connected to another transformer i use for my 30V dc power supply. Because it's galvanic separated it should work i think. I've got another digital meter based on the icl7107 wich i bought somewhere. That one is still working. The voltmeter i bought broke down because i didn't have a galvanic seperation back then. edit: I used a 2k trimmer and it didn't change a thing. I still don't know what they mean with the 200mv scale and 2V scale. Does it mean when i use a 12k resistor for 0-200V i should use the 2V scale to get xxx.x reading? So the 2V scale has 2000 steps and the 200mv scale has only 200 steps? At the moment i have a 470k resistor for 2V scale, a 12k resistor for 0-200V. And the rest of the components is exactly the same as in the datasheet. I have no clue why the icl7107 measures 2,63 times less than the actual value. edit2: i changed the 470k resistor to a 47k resistor, no change at all. Still a solid 0.6V while it should read 1.58. Someone on posted his project on the eagle website, he had no link between pin 30 and 32 but that's even worse for me. My soldering station also broke down so i'm really getting frustrated. I checked all the connections and i checked the datasheet, i can't find any error in my design.
  5. Yes i did. I'm going to look at the datasheet, see if i'm missing something, and also try out the 100k oscillator resistor. edit: 100k resistor didn't change anything. edit2 : The icl7660 ic is working normal. I did some new measurements : Battery is 1,58V, icl7660 shows 0,6V. It's a ratio of 2,633 and i can't find any component that's 2,633 times different than the correct value. Also in the datasheet they specify a 1k trimmer, on this website it says a 20k trimmer. When regulating the trimmer i don't notice any difference, so i'm guessing this may be the problem. If i change to a 1k trimmer i can adjust the reference so it shows the actual value. Or am i wrong? In the datasheet they also mention a 200mv scale and a 2V scale, what does this mean? Is the measured voltage divided to a 0-2V scale? The datasheet also says vref should be 1V if the scale is 2V. So for vref to be 1V i have to set the trimmer correct, and then it will show the correct value on the led display?
  6. I took out the damaged icl7107 and replaced it but for some reason everything i measure is more or less half of the actual value. My battery is 1,3V and my meter shows 0,6V. When i couple two battery's it shows 1,2V. So it's measuring now, but it measures half of the actual value. Playing with the trimmer didn't help. I'm going to change the oscilator resistor from 180k to 100k tomorrow.
  7. Hello everyone, i've got a problem with my voltmeter. I just finished it and it shows 18.4V when i don't measure anything. It shows 1xxx when i measure a 1,5V battery and when i switch the wires it shows -1xxx. So it looks like it can detect when you switch + and -. When i hold the measuring points together it shows 00.0. So it looks like i have a problem with my scale, although i used a 12k resister and i only measure a 1,5V battery. I used the exact same components as mentioned on the website but i use standard resistors instead of the 1% accuracy ones. Does someone know what might be the problem? Thanks in advance. Bart edit: i use a 180k resistor at pin39 instead of a 100k resistor. I see pin39 has something to do with the oscillator. Could this be the problem? edit2: i think i broke it :p. I saw 2 errors in my voltmeter. I use an experiment pcb with pre drilled holes because i don't have the equipment to etch and stuff. And it also has to fit into a 70mm x 39mm case so i'm making it super compact. I used to work on it during school about a year ago and now during the vacation i wanted to finish it. Some wires got loose and i soldered it onto the wrong place. Errors : +5V was directly connected to pin 31 of the icl7107 ic. The 1M resistor was connected between pin 31 and 30 instead of in series. The elco connected to pin 5 of icl7660 was inverted because it's wrong in the schematic. I did some measurements after the corrections: Between pin 3 and 5 of the icl7660 i measure +2,57V and between pin 3 and 5 i measure -7,45. So i guess the icl7660 is broken now? I did new measurements, i get the correct +5V and -5V from the icl7660. So i guess the ICL7107 is broken. My leds now only show 00.0 and it doesn't even see if i switch + and - anymore. I'm going to check tomorrow for more errors, going to bed now.
  8. No, i think that is correct. I'm going to buy an ICL7660 ic soon and test it out. I've been searching on the internet and it turns out that the ICL7107 does need a negative supply.
  9. I posted my pcb a few threads back, these are the pictures of the case i promised. The front, one digital voltmeter broke because i didn't have a galvanic isolated supply for it. I'm building my own now, pictures of it are below. There are 2 leds, one for the current limitter and one wich glows green when the fuse is ok and red when it's blown. The little switch next to the red switch is to turn the fan on, i'm searching for a broken pc supply to get it's fan regulator. The side, you can see the fan. [img width=680 height=510] At the back i used this socket to power the power supply. [img width=680 height=510] I only have one 2N3055 because i only got one heatsink. The top pcb is the power supply, the pcb beneath it is a 5V supply for my displays. I need to modify it so it can also supply -5V. On the top pcb is also a little transformer mounted because i needed galvanic isolation for my meters. When closed the fan blows directly on the 3 heatsinks. [img width=680 height=510] You can see the two big electrolytic capacitors beneath the power supply pcb. [img width=680 height=510] My self made digital voltmeter. It's vacation and i don't have the equipment to make a pcb like in school so it doesn't look that good but it gets the job done. [img width=680 height=510] [img width=680 height=510] Mounted in the case of the broken meter. [img width=680 height=510] [img width=680 height=418] I made this supply for my latest school project. I haven't used it yet but it regulates between 0 and 29V with all trimmers unregulated. So i think i can push more out of it.
  10. I'm building this digital voltmeter with an ICL7107. http://electronics-diy.com/ICL7107_volt_meter.php I left away the negative voltage supply and just connected the ground to pin 26. I thought the negative voltage isn't needed when you only measure positive voltages. However, my display only shows zero's now. When i measure a voltage the display show a few numbers fast and then goes back to zero's. I'm guessing this is because i don't have the negative supply? Could someone verify that? And i heard that you need 2 seperate supply's wich are galvanic isolated from each other and the measuring voltage if you use 2 ICL7107 meters, is this correct? I wanted to search this thread but all the posts have this written in it : "Message is not available". Thanks in advance.
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