Cheap Source of Panel Meters? - Page 1
Forum section: electronics / beginners

author: krivx
author_rank: Frequent Contributor
timestamp: July 30, 2012, 03:05:59 pm
content: Not sure if this belongs here, but I'm certainly a Beginner when it comes to these kind of meters.I have a 4a Variac with no indicator of output voltage or current apart from the uncalibrated scale on the voltage adjustment knob. I would like to add some panel meters so I can monitor what's it doing without tying up a couple of multimeters. I've shopped for meters on Farnell and Radionics/RS and found that meters tend to be much more expensive than I had expected. Ebay is awash with cheap Analog and Digital solutions but I obviously I have no idea as to their quality.Can anyone recommend a model or specific range? I just need to measure 0-275VAC with reasonable accuracy (5% would be a fine) and a similar crude current measurement over a 0-4A range. I would like to do this without spending much more than 20e/meter if possible. I don't care if I need to add a 5V supply for a digital meter.

author: saturation
author_rank: Super Contributor
timestamp: July 30, 2012, 05:01:44 pm
content: A simple quick solution is get a premade analog 'line voltage' meter like this:You plug it into an open socket on the variac, then plug the DUT to it. It has its obvious limitation such as scale, resolution etc., but its fast to implement.I use the killawatt with my variac's built in meter, so I can monitor power consumption, but its bulkier and you need an extension cord because the killawatt blocks other available sockets when its plugged into the variac:

author: mianchen
author_rank: Regular Contributor
timestamp: July 30, 2012, 05:37:35 pm
content: Quote from: Electroalek on July 30, 2012, 03:31:14 pmThat's what I was thinking something like this infamous DT-830:£4 incl. postage, cheaper than a 16 x2 character LCD display ....

author: krivx
author_rank: Frequent Contributor
timestamp: July 30, 2012, 05:46:15 pm
content: Not sure if those DC analogue meters will give a meaningful RMS measurement when fed with 50Hz...Cutting up a cheap meter might work but finding a matching bezel for panel mounting could be a hassle.http://www.ebay.ie/itm/330743180589?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649This looks good but I'm a little confused as to the 80-300VAC spec - not sure why the measurement would bottom out at 80V. Included current transformer is nice, I would like finer resolution on the current read-out but could live with this.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 30, 2012, 06:10:53 pm
content: Quote from: krivx on July 30, 2012, 05:46:15 pmGood point, could rectify the output, add a small cap, divide the voltage by 10(string of resistors), then use a $2 voltmetre often used for cars and testing battery charge, so if it says 10.1, you're actually getting 101v.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 30, 2012, 11:14:13 pm
content: first time i bought 1 similar to this...http://www.ebay.com.my/itm/Mini-DC-0-99V-3-Wire-Voltmeter-Blue-LED-Display-Volt-Meter-Digital-Panel-Meter-/300750911491?pt=LH_DefaultDomain_2&hash=item460626b803put it in my crappy PSU and then i order another ten, havent found any use for those yet. 0-99V only maybe hackable. YMMV.

author: cwalex
author_rank: Frequent Contributor
timestamp: July 31, 2012, 11:59:49 am
content: This site has some reasonably priced panel meters that look quite nice. They are designed to press into a rectangular hole so not too hard to cut a hole roughly the right size and just press it in.http://www.sureelectronics.net/category.php?id=2&price_min=0&price_max=0&filter_attr=&page=2&sort=goods_id&order=DESC

author: Monkeh
author_rank: Super Contributor
timestamp: July 31, 2012, 01:41:49 pm
content: Quote from: Mechatrommer on July 30, 2012, 11:14:13 pmI bought a similar unit. Claimed 1% accuracy is a laugh, they're nowhere near that accurate (or usefully accurate at all, imo). That looks to be exactly the same device with a slightly different PCB layout. Same totally unmarked IC. Waste of money.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 31, 2012, 01:47:24 pm
content: yes the reading are sparsed, accuracy is not the main priority with this cheapo, but i believe quite handy for project that need reading onthego instead of hacking fullblown big size DMM for a particular purpose. i believe some tweaking is needed to make the reading acceptable.

author: Monkeh
author_rank: Super Contributor
timestamp: July 31, 2012, 02:00:17 pm
content: Quote from: Mechatrommer on July 31, 2012, 01:47:24 pmUnfortunately only acceptable for a small range. I was able to get anything between 10V and 30V to be accurate to one digit. Above or below that it went out by up to 30%. I got refunded and scrapped it for the 7-segment display.

author: T4P
author_rank: Super Contributor
timestamp: August 01, 2012, 02:00:42 am
content: Well isn't it 7 segment also ?I have one of these self powered ones with 3.2-30Vthat is within 1% ...

author: Monkeh
author_rank: Super Contributor
timestamp: August 02, 2012, 01:39:17 pm
content: Quote from: mianchen on July 30, 2012, 05:37:35 pmIt is? I got one shipped from within the UK for £2.50 and from China for £1.50.Quote from: T4P on August 01, 2012, 02:00:42 am.. Yes, the crap, useless panel meter had a 7-segment display. The only useful part on it.

author: T4P
author_rank: Super Contributor
timestamp: August 02, 2012, 02:35:38 pm
content: Quote from: Monkeh on August 02, 2012, 01:39:17 pmMine is useful only from 4.48V onwards ... anyway it's rated at 30V so it's a POSAh well, probably going to use it as a 5V supply monitor anyway

author: T4P
author_rank: Super Contributor
timestamp: August 02, 2012, 11:33:20 pm
content: @Monkeh Sureelectronics sells a unimaginable amount of decent panel meters

author: silicon_ghost
author_rank: Contributor
timestamp: August 08, 2012, 12:38:56 am
content: Check out Light Object's collection for accurate voltage and current meters (http://www.lightobject.com/Search.aspx?k=4.5%20digital%20meter). The link limits you to the accurate models. Search around on the site (or their eBay storehttp://stores.ebay.com/coldfusionxelectronics) for other panel meters they offer.I did a quick test of the 2VDC model on my bench and posted it in the review section of eevblog:https://www.eevblog.com/forum/product-reviews-photos-and-discussion/coldfusion-4-5-digit-led-2v-panel-meter/

author: krivx
author_rank: Frequent Contributor
timestamp: August 08, 2012, 06:05:20 pm
content: Quote from: silicon_ghost on August 08, 2012, 12:38:56 amThese look nice, I'm guessing they are an ICL7135.I actually have quite a few 7segment LED displays lying around so right now I'm toying with the idea of assembling an attenuator -> RMS-DC converter -> A/D -> 7 segment display configuration. I was thinking of getting a cheap current shunt but hall effect sensors that can measure ~amps aren't too expensive. Building this myself probably won't be the cheapest solution but I like the idea of getting exactly the features I want, including a fun project.