Author Topic: I have a short in my first project ugh!  (Read 7250 times)

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Offline wblackledgTopic starter

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I have a short in my first project ugh!
« on: April 12, 2015, 12:16:49 am »
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.jpg

I 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!   :box:
 

Offline android

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Re: I have a short in my first project ugh!
« Reply #1 on: April 12, 2015, 12:31:32 am »
Can you post pics of your board (top and bottom)?
Lecturer: "There is no language in which a double positive implies a negative."
Student:  "Yeah...right."
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #2 on: April 12, 2015, 03:56:18 am »
Can you post pics of your board (top and bottom)?

Yes, here you go.

that mess on the right side of the back is my positive rail made from solder.  :palm:

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)  ;D

the LEDs are on another board and I used headers to connect them.  (that board seems to work, well light up as expected).
« Last Edit: April 12, 2015, 04:05:44 am by wblackledg »
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #3 on: April 12, 2015, 03:57:36 am »
Might be solder flux leakage current. Try put weak pull down resistors at every input pin of uln2004.

does flux carry current?

thanks.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #4 on: April 12, 2015, 04:22:31 am »
Flux carries tiny amount of current, and that is more than enough to affect unterminated input pins.

ugh, well from the photo you can see I have more than enough flux. 

Is there an easy way to clean it up?
 

Offline Evil Lurker

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Re: I have a short in my first project ugh!
« Reply #5 on: April 12, 2015, 06:54:57 am »
Flux carries tiny amount of current, and that is more than enough to affect unterminated input pins.

ugh, well from the photo you can see I have more than enough flux. 

Is there an easy way to clean it up?

91% alcohol and an old toothbrush.
 

Offline android

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Re: I have a short in my first project ugh!
« Reply #6 on: April 12, 2015, 07:28:07 am »
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.

Lecturer: "There is no language in which a double positive implies a negative."
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Offline mrflibble

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Re: I have a short in my first project ugh!
« Reply #7 on: April 12, 2015, 08:26:47 am »
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."
 

Online Mechatrommer

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Re: I have a short in my first project ugh!
« Reply #8 on: April 12, 2015, 11:49:22 am »
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...
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Offline Zero999

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Re: I have a short in my first project ugh!
« Reply #9 on: April 12, 2015, 12:56:04 pm »
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.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #10 on: April 12, 2015, 01:52:48 pm »
Flux carries tiny amount of current, and that is more than enough to affect unterminated input pins.

ugh, well from the photo you can see I have more than enough flux. 

Is there an easy way to clean it up?

cool. thanks.  I only have 70% around the house, so I'll have to pick some up.

91% alcohol and an old toothbrush.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #11 on: April 12, 2015, 02:05:30 pm »
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.

I 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.  :-DD

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.   :D
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #12 on: April 12, 2015, 02:09:37 pm »
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.


yes, I think version 2.0 (assuming I can't figure out the problem in this 1.0 ver)  will have a wire rail and not solder blobs..  ^-^
IPA? (India Pale Ale)?   ;D  I'll have to look up what that is.. thanks.

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."
 

Offline janoc

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Re: I have a short in my first project ugh!
« Reply #13 on: April 12, 2015, 02:13:01 pm »
Flux carries tiny amount of current, and that is more than enough to affect unterminated input pins.

Flux 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.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #14 on: April 12, 2015, 02:15:02 pm »
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...

thanks, 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.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #15 on: April 12, 2015, 02:16:16 pm »
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.

No, but I was planning on using aluminum wire for the probes in the sump.  will that help?

thanks.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #16 on: April 12, 2015, 02:23:30 pm »
Flux carries tiny amount of current, and that is more than enough to affect unterminated input pins.

Flux 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.

thanks.  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..  :P

 

Offline mrflibble

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Re: I have a short in my first project ugh!
« Reply #17 on: April 12, 2015, 04:23:10 pm »
yes, I think version 2.0 (assuming I can't figure out the problem in this 1.0 ver)  will have a wire rail and not solder blobs..  ^-^
IPA? (India Pale Ale)?   ;D  I'll have to look up what that is.. thanks.
IPA = Isopropyl alcohol.
 

Offline KJDS

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Re: I have a short in my first project ugh!
« Reply #18 on: April 12, 2015, 04:51:05 pm »
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.

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #19 on: April 12, 2015, 05:21:06 pm »
yes, I think version 2.0 (assuming I can't figure out the problem in this 1.0 ver)  will have a wire rail and not solder blobs..  ^-^
IPA? (India Pale Ale)?   ;D  I'll have to look up what that is.. thanks.
IPA = Isopropyl alcohol.

ah!  ok. thanks.  I bought 91% alcohol and acetone at Walgreens this morning.  I'll give it a shot and let you know.

thanks.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #20 on: April 12, 2015, 05:22:03 pm »
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.

that does help. Since I'm a software guy, I'm sort of looking at this as a program with no backspace/delete key..  ^-^

 

Offline Evil Lurker

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Re: I have a short in my first project ugh!
« Reply #21 on: April 12, 2015, 06:56:51 pm »
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.

that does help. Since I'm a software guy, I'm sort of looking at this as a program with no backspace/delete key..  ^-^

If 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. I

And 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.
 

Offline wblackledgTopic starter

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Re: I have a short in my first project ugh!
« Reply #22 on: April 13, 2015, 12:51:35 am »
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.

that does help. Since I'm a software guy, I'm sort of looking at this as a program with no backspace/delete key..  ^-^

If 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. I

And 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.

yeah,  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)..  :-+
 

Offline GreyWoolfe

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Re: I have a short in my first project ugh!
« Reply #23 on: April 13, 2015, 01:35:44 am »
yes, I think version 2.0 (assuming I can't figure out the problem in this 1.0 ver)  will have a wire rail and not solder blobs..  ^-^
IPA? (India Pale Ale)?   ;D  I'll have to look up what that is.. thanks.
IPA = Isopropyl alcohol.

India Pale Ale tastes better.
"Heaven has been described as the place that once you get there all the dogs you ever loved run up to greet you."
 

Offline KJDS

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Re: I have a short in my first project ugh!
« Reply #24 on: April 13, 2015, 09:51:51 am »
yes, I think version 2.0 (assuming I can't figure out the problem in this 1.0 ver)  will have a wire rail and not solder blobs..  ^-^
IPA? (India Pale Ale)?   ;D  I'll have to look up what that is.. thanks.
IPA = Isopropyl alcohol.

India Pale Ale tastes better.

I recently wasn't paying attention when I diluted some screenwash and used IPA instead of water. Fortunately I only wasted solvent, not beer.


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