What could cause not only three outputs in a row to fail, but to all short together? All I did was solder a wire to each power an led thru a 220ohm resistor,
if I powered one up the leds would all be lit dimly, another not at all, and the last would light up all three bright
could it have been het that killed this? Or is this just my unlucky batch from ebay?
As long as you have not wired pin 9 to anything, and have wired everything up correctly and not left any inputs floating then it could be a faulty chip.
I guess that's it, sucks because I didn't know it was faulty until everything was done and replacing dip ics are kindaa hard
maybe ill buy it next time from an actual supplier or use sockets : /
replacing dip ics are kindaa hard
Here is a tip. The chip is dead so just take a small pair of side cutters and cut all the leads right next to where it goes into the plastic. So the body falls off.
Then you can extract the pins one at a time from the board.
A lot easier than trying to remove the chip whole.
That is definitely a good idea, taking one pin out is the easiest
thx
Grumpy_Mike:
As long as you have not wired pin 9 to anything, and have wired everything up correctly and not left any inputs floating then it could be a faulty chip.
Not to anything?
The ULN2803's pin 9 should be connected to Ground (Gnd, GND.)
[Its pin 10 can be left unconnected, it's the flyback diodes' COMmon, which would go to +V.]
I didn't wire the ommon and did wire the gnd lol
As a general rule, even if bought at FlyByNite Electronics, the probabilities for
a circuit not working are probably in the range of .... 98% operator error,
2% bad chip.
I cannot remember the last time I bought a chip that was actually bad out of
the box, but probably 75% of the ckts I jigger up don't work the first time.
If I burnt it it would be the first ic that I've done it too, in about the year I've been doing this
unless the transistor array is more susceptible to heat, idk why other than bac chip three pins shorted together internally
What were the input pins connected to?. Not I hope open flying or loose wires, one of the three variants of theULN28XX devices has a high enough input impedance to oscillate and If you have no bypass capacitor next to that! chip (Required as it switches heavy loads) then the whole chip might be oscillating. After having a close look at the data sheet the only way that chip could break would be if you exceeded the collector current of the outputs that have failed, a momentary short to the LED supply when the device was powered up and working would cause this and it might have been one output that 'killed' all three, Are they consecutive... adjacent to each other???.
If Not then perhaps there are other issues and I would either check Very carefully or install a socket... But remember the PCB is the heat-sink for that device. IMO
Doc
unless the transistor array is more susceptible to heat, idk why other than bac chip three pins shorted together internally
Those chips are really meant for industrial applications, so they are probably fairly
robust in [proper :-)] operation, meaning sans "operator error".
Also, I have no idea what your sentence means starting with "idk ...". ????
Sorry typo, meant bad chip
they are next to each other, driving leds at 5v, 20ma each
Its the one with 2.7k input impedance, which went through a 1k resistor to a shift register, all which I checked for shorts before powerup
Im pretty sure I didn't short them out, the only thing about the three pins is I didn't have leds hooked up to them at first,
it is just a weird failure mode where two of the pins would light up both leds dimly, and the third would light it up entirely but not the one it was supposed to(actually caused by voltage drop of the transistor because a slightly higer vcc would light it up the same as the other two
After having a close look at the data sheet the only way that chip could break would be if you exceeded the collector current of the outputs that have failed, a momentary short to the LED supply when the device was powered up and working would cause this and it might have been one output that 'killed' all three,
I agree, this is probably about the only way to kill the output ckts, as they are meant
to drive 600-mA [I forget exactly], but to be in saturation at the same time, ie, the
collectors are not meant to be at 5V when the current is max.
The ULN2803's pin 9 should be connected to Ground (Gnd, GND.)
[Its pin 10 can be left unconnected, it's the flyback diodes' COMmon, which would go to +V.]
Yes sorry at the time I was looking at the data sheet for the ULN2003, and pin 9 is the diode rail on that one.
The outputs weren't shorted, just the inputs actually
idk if it changed while power was on but I found that strange since there's no way I couldn't damaged that unless I burnt it
For a quick answer that might be rather technical... a section (1 of 8) of a ULN2803 is a 2K7 resistor one end open (input) the other end to an internal base connection (anode of a diode) the emitter of that transistor (cathode of that diode) connects to the base of the second transistor of the driver (anode of a diode) and the emitter of that (second) transistor (cathode of a diode) goes to ground... so we have a component series string of parts each diode has a resistance of .7 volts (for simplification as we all know that resistors don't behave that way) for examination... I modeled it that way... 2 X .7V + 2.7K in series... the ULN2803 has some device limits that are important... 1, 500mA Max per output 2. 2500mA total or max emitter/substrate current (substrate is ground) from that there can only be 5 outputs on @ full (500 mA load) and 3. 30 V max input voltage on any input pin (outputs are 50V max open circuit voltage, above this the transistor {output} will avalanche or break down Very destructively). I have seen them explode, quite literally blew the top half of the case off and stuck it into the acoustic ceiling tiles.
This means that in order to break the ULN2803 by (Shorting the inputs) you would probably need in excess of 30 v and probably more like 40 - 45 V at any input pin... In short it is very unlikely that you broke/bricked the device by 'shorting' inputs as that kind of voltage would be very unlikely to be present, particularly from an Arduino of any 'flavor' and VERY PROBABLE that you shorted an output to VLEDsupply I don't know how much each led 'string' requires in your project but from what you describe totally, it wasn't an input but rather an output that was enabled or on at that time and shorted to something that could supple about 2 amperes.
The ULN2803 is a designers dream... used within it's limits I have found it (I used MANY MANY of those devices as relay/solenoid drivers) to be nearly indestructible... Except on breadboarded development circuitry where sh*t (stuff) can and all too frequently does... In My Direct Experience...
Always keep this in mind... Murphy was an optimist... IMO
Data sheets are written for a purpose and with a little thought even a complete NOOB can figure out some of the basics... SO READ THEM B4 U use a part...
Doc
Actually, now that I think about it my laptops usb power can't suppply more than 500ma, and the arduino would have shut down from the voltage dropping so much( it actuaally goes below 2v with like 400ma draw, that's why I added a 4700uf cap to keep things smooth
I would seriously think about an external 7.5 - 9V supply, It's the only way I power anything except the Arduino itself. I only tie the grounds together... there is one I found that can be 5V on one set of rails and 3V3 on the other... With a jumper for each side and a power switch - power led. All sources supposedly @ 1 A each. Fits on the 830 tie point and hits both set of power supply rails. It was 3+ dollars from Ebay. Yeah I know that there are faster places but... a dollar is a dollar. I can be patient for 50% differences in price. or more. IMO
Doc
I have plenty of supplies, it just happen to be what I was plugged into for testing
I have a nice 5v 3a supply off ebay
How does that breadboard thing work? I've seen them but kinda curious on their power and usefulness
Very well as a matter of fact. There are two types and should be a third W/ a Switcher... but I digress, again... the first one will fit any breadboard whether it has two supply rails (blue and red stripes) or the more common single rail and it will supply 3V3 or 5V to both rails. It has enough pin holes for either configuration. The second type is only really for the dual rail board. It Will supply either 3V3 or 5V to either rail. Both have 1A low dropout linear regulators. I also use the ""Extension shield/cable & header" device that Liudr sells on Inmojo and Dipmocro (Ebay). It is basically a good part, Very useful for making sketches work with parts/sensors with one short coming and that is the lack of provisions for bypassing and an external power supply for heavy loads. I have one of those 1.8" TFT displays from Adafruit (good place/product as it worked first time W/O hassles) however the back light causes a .5V drop in the breadboard 5V source so I use another really cheep part and it fixes all the issues. Just Don't forget to connect the grounds of the board and PSU. IMO
Doc