I have a short in my first project ugh! - Page 1
Forum section: electronics / beginners

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 12:16:49 am
content: Hi,So I'm following this design of a water level circuit. (see below)http://www.bdspeedytek.com/wp-content/uploads/uln2004-water-level-indicator.jpgI bread boarded it, and it works, but once I put it on perfboard and soldered it, it doesn't work, and the multimeter continuity test has it beeping almost everywhere I connect the probes.I put the positive probe on the positive "+ 9 to 12v " area shown in the upper right corner of the schematic and the negative problem on the left side of each of the 47K resistors and the meter beeps on all but one 47k resistor. Dont' know if this is the problem for the entire circuit or not? Voltage is showing 9V (which is what I have the PS set to) on all as well. Better question, should it beep? The common probe and the contact wires are open (not connected, not in water).please dope slap me please!

author: android
author_rank: Regular Contributor
timestamp: April 12, 2015, 12:31:32 am
content: Can you post pics of your board (top and bottom)?

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 03:56:18 am
content: Quote from: android on April 12, 2015, 12:31:32 amYes, here you go.that mess on the right side of the back is my positive rail made from solder.anyway, my first attempt at any type of circuit board soldering since 1971 when my brother and I put together a radio shack kit metal detector. (which paid for itself as we dug around the city parking meters)the LEDs are on another board and I used headers to connect them. (that board seems to work, well light up as expected).

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 03:57:36 am
content: Quote from: blueskull on April 12, 2015, 02:45:34 amdoes flux carry current?thanks.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 04:22:31 am
content: Quote from: blueskull on April 12, 2015, 04:21:31 amugh, well from the photo you can see I have more than enough flux.Is there an easy way to clean it up?

author: Evil Lurker
author_rank: Regular Contributor
timestamp: April 12, 2015, 06:54:57 am
content: Quote from: wblackledg on April 12, 2015, 04:22:31 am91% alcohol and an old toothbrush.

author: android
author_rank: Regular Contributor
timestamp: April 12, 2015, 07:28:07 am
content: I don't want to sound impolite but I'd start again with a fresh piece of perf board - preferably one where the coordinate markings are the same on both sides. In your photos, T14 on the top side is marked as A14 on the bottom (why did they do that).Then I'd keep all the resistors spaced inline with the IC pins. I notice you're only using 6 out of the 7 drivers (unlike the circuit diagram) so you could just leave one unconnected I guess. This should make it a lot easier to figure out the wiring pattern you need and saves you from having to solder diagonal bridges.The odd-man-out reading was probably the resistor going between A13 and D13 (top) which is bridged on the bottom to E12 (top)...but E12 is not connected to anything as far as I can tell.

author: mrflibble
author_rank: Super Contributor
timestamp: April 12, 2015, 08:26:47 am
content: Some of the solder blobs on the backside are a weeee bit big. It's hard to see on the photo, but there are several spots that look like they could be shorts. Apply some flux and remove excess solder with some solder wick. Mostly in the P,Q and L,M columns. And then clean it up as suggested with ye olde solvent + toothbrush. If you don't have rubbing alcohol you can use something more aggressive in a pinch, as long as you clean that up as well. Some warm water with soap works fine for that, and then blow dry it with the human powered blower. Of course using IPA is nicer than say kerosene, but just suggesting that you don't have to be too picky about what solvent to use for a first job since you might not have collected all the goodies yet. After you get this job done you can get some IPA for the next projects.About that positive rail made of solder ... to avoid that you can use a piece of fairly thick solid copper wire. Strip it, pre-tin it and then use that as a power rail instead of the mountains of solder. Or if you have some cheapo bare copper clad, cut a strip of said copper claid, super clue it to the perfboard and use that as power rail. Also makes for easy mounting of some decoupling caps where needed.And it indeed looks like the manufacturer messed up the numbers on the top vs bottom side. "What? Spend 5 more minutes?Copy/paste silkscreen."

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 12, 2015, 11:49:22 am
content: this is the kind of "talk nonsense" or "not enough info provided". how can you make short across a resistor? either your resistors are damaged or you perfboard is causing the short, maybe there is 3rd layer trace that connecting all columns in each row? btw, keep practising soldering. you have too much solder there...

author: Zero999
author_rank: Super Contributor
timestamp: April 12, 2015, 12:56:04 pm
content: Go round with a solder sucker and remove the excess.I hope you're aware that using DC for sensing water can cause corrosion problems in the long term.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 01:52:48 pm
content: Quote from: Evil Lurker on April 12, 2015, 06:54:57 am

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 02:05:30 pm
content: Quote from: android on April 12, 2015, 07:28:07 amI actually considered starting over, with a larger board. I didn't notice these boards were mis-printed until I started to try and debug them. I guess thats why they were so cheap on ebay from china.I didn't use a few of the some of the drivers because its for a small sump pump well, so I only needed a few indicators.thanks, I'll give it a cleaning, and take another look but if I can't figure it out I'll start over.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 02:09:37 pm
content: Quote from: mrflibble on April 12, 2015, 08:26:47 am

author: janoc
author_rank: Super Contributor
timestamp: April 12, 2015, 02:13:01 pm
content: Quote from: blueskull on April 12, 2015, 04:21:31 amFlux alone would not make his meter beep. That needs way lower resistance.Most likely some solder bridges somewhere. Also, it isn't clear where exactly were the probes put - the meter could make the input clamping diodes of the IC open and it could indicate as a short. Hard to say without knowing exactly how it was measured and which meter was used.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 02:15:02 pm
content: Quote from: Mechatrommer on April 12, 2015, 11:49:22 amthanks, I realize its hard to describe, and I wasn't expecting anybody to debug it remotely via a web forum, just thought some people could come up with common problems with noobs (like too much solder) that might cause the problem I'm having.thanks again.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 02:16:16 pm
content: Quote from: Hero999 on April 12, 2015, 12:56:04 pmNo, but I was planning on using aluminum wire for the probes in the sump. will that help?thanks.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 02:23:30 pm
content: Quote from: janoc on April 12, 2015, 02:13:01 pmthanks. the brown wire would and pink wire would be one of the probe connections. the rest would be in the headers once fully working. I was using the the brown wire to test each driver/probe. including the other board that contains the LEDs. none worked. ugh..

author: mrflibble
author_rank: Super Contributor
timestamp: April 12, 2015, 04:23:10 pm
content: Quote from: wblackledg on April 12, 2015, 02:09:37 pmIPA =Isopropyl alcohol.

author: KJDS
author_rank: Super Contributor
timestamp: April 12, 2015, 04:51:05 pm
content: If it's any consolation, it's normal for a circuit not to work when you build it. Usually the mistake, once found, is obvious, however sometimes it takes a lot of searching to find it.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 05:21:06 pm
content: Quote from: mrflibble on April 12, 2015, 04:23:10 pmah! ok. thanks. I bought 91% alcohol and acetone at Walgreens this morning. I'll give it a shot and let you know.thanks.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 12, 2015, 05:22:03 pm
content: Quote from: KJDS on April 12, 2015, 04:51:05 pmthat does help. Since I'm a software guy, I'm sort of looking at this as a program with no backspace/delete key..

author: Evil Lurker
author_rank: Regular Contributor
timestamp: April 12, 2015, 06:56:51 pm
content: Quote from: wblackledg on April 12, 2015, 05:22:03 pmIf it makes you feel any better I about tore my brains out trying to figure out what was wrong with an LM317 circuit that I built... turns out that there was nothing wrong with the PCB circuitry, it was the LM317's I had purchased off Ebay were all fakes and they were from a USA based seller at that. IAnd for what I is worth I didn't bother with requesting a refund or initiating a paypal dispute, but for the time I wasted and the headache it caused me I sure as hell slapped them with a negative feedback.

author: wblackledg
author_rank: Regular Contributor
timestamp: April 13, 2015, 12:51:35 am
content: Quote from: Evil Lurker on April 12, 2015, 06:56:51 pmyeah, even distributors get stuck with fake crap from time to time. all of this stuff came from digikey.I've moved on. I decided to start over and am almost done. I tested the first probe and it worked! yay! (as my daughter says)..

author: GreyWoolfe
author_rank: Unknown
timestamp: April 13, 2015, 01:35:44 am
content: Quote from: mrflibble on April 12, 2015, 04:23:10 pmIndia Pale Ale tastes better.

author: KJDS
author_rank: Super Contributor
timestamp: April 13, 2015, 09:51:51 am
content: Quote from: GreyWoolfe on April 13, 2015, 01:35:44 amI recently wasn't paying attention when I diluted some screenwash and used IPA instead of water. Fortunately I only wasted solvent, not beer.