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Forum Index : Electronics : LCD Panel meters
| Author | Message | ||||
| Arthur Newbie  Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Good day, |Well this morning I received 2 of the above meters. They had a wraper round them saying that the supply voltage had to be isolated from the measured voltage/amps. Well as there was nothing in the advert about this I didnt think it applied. So I have read the gentlemans reference to this on this web and his way of getting round it. Unfortunatly I dont have a board with the requiered chip on it.I wonder if or how its possible to generate an isolated power for these things? Any assistance greatfully received. Arthur |
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Google for 'LCD panel meter isolated power supply circuit' and the 1st and 4th hit will give you the circuits you're looking for. Haven't bothered to check out the rest of the hits, this is left as an exercise for the reader. 9V battery and an on/off switch work too. Peter. |
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oztules Guru  Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Arthur A simple multivibrator circuit like this could use the little driver transformer from an at or atx power supply, and a much simpler output bridge..... don't get much simpler than that. Picture from above link 
.........oztules Edit: Got distracted part way through the above post(cup of coffee with the boss) and so didn't see Dinges relpy till I got this posted... beaten again  Village idiot...or... just another hack out of his depth |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Many thanks to you on Flanders Island, I had googled and found papers and circuitry that filled a double A4 pages, not what I was hoping for!!! I beleived you used a chip off an ethercard which I read some time ago but no card in my junk box. you have saved the day agein many thanks from the othe island. |
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| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
Also many of the add on ethernet controllers for isa and pci bus feature nice isolating 5V to 9VDC converters.. could be useful if you have those boards lying around. If at first you don't succeed, try again. My projects |
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sPuDd Senior Member Joined: 10/07/2007 Location: AustraliaPosts: 251 |
Glenn did such a project and posted it on the front page: LCD Panel Meter Interface sPuDd.. It should work ...in theory |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Yes I had seen that article, unfortunatly I dont have a board with that chip on. Arthur |
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| sPuDd Senior Member Joined: 10/07/2007 Location: AustraliaPosts: 251 |
You can make one as Oztules said. The transformer can be scrounged from almost anything, or just by a mini audio transformer from the local electronics shop. Build the cct on vero board and drive each transformer till you find one that produces the results you want. The power levels are so low you would have trouble causing smoke. sPuDd.. It should work ...in theory |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Thank you have sourced a couple of snall transformers from a p.c. psu which as Oztules should do the job, thanks, Arthur |
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| greybeard Senior Member Joined: 04/01/2010 Location: AustraliaPosts: 161 |
Bit of a grave dig I'm afraid but I had problems with the old forum and not being able to log in. Just want to make mention of a potential issue with the LCD panel meter project. I have a similar setup but I decided I wanted to have positive rail current monitoring ( to avoid earthing issues with vehicles ). If you don’t have separate power supplies for the LCD’s you will destroy one of the LCD’s. I took one out and then tried again with the test power supply current limited and there is something inside the LCD’s that causes a failure if the current shunt is on the positive supply. I eventually used a different supply. Basically a cmos oscillator with some inverters but I AC coupled the inverter output into two separate rectifier circuits and used these to power the LCD’s. ie, two seperate isolated DC supplies, one for each LCD meter. I used the different supply as I use it to monitor some solar panels for when I'm camping and i wanted to reduce the quiescent current as much as possible. I also wanted the meter to use the measured supply for power. See bottom of this page for basic cct. simple isolated supply I just duplicated the right hand side of the cct from the 100nF caps to give me the two isolated supplies I needed. It’s working well. |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Another way is to use an isolated DC to DC converter. I used a tiny 12V to 5V converter from Altronics, works a treat, was relatively inexpensive and fits nicely inside the panel meter box. On my boat I used a 9V battery/ 5V regulator combination with a push to measure button as the meter reading is only checked occasionally. There are 2 100A shunts (one for each battery) and a selector switch so just one panel meter can monitor the charging or drain on each battery. Klaus |
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| greybeard Senior Member Joined: 04/01/2010 Location: AustraliaPosts: 161 |
Another method I experimented with was using a DPDT momentary action switch and a large electrolytic capacitor ( 4700uF or larger ). You wire up the switch with the 12V supply to the 'off' side of the switch, the electro cap to the 'common' and the LCD panel meter to the 'momentary' of the switch. Then you operate the switch to the 'momentary' side and the electro will power the LCD meter for several 10's of seconds while you take the reading. You never need to worry about a flat battery. This also works very well and is a usefaul technique for low current drain ccts that require isolation from the powering source and are only required to operate for short periods. My driver was low current drain and low cost. The original design on this website had a greater quiescent current drain than I was happy with. Same with the majority of commercial 12v to xxV isolated supplies I could find. |
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| Alasdair Regular Member  Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi all I made a similar meter work using a 555 running as an astable oscillator into a tiny audio transformer, then half wave rectified the secondary and filtered it with about 22uf and a five volt Zener. The whole circuit used about 2 milliamps and has been working for years. I think it ran at about 10khz but isn't critical. Regards Alasdair. Amc-elec |
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