Hello I've been intrested in making one of those led bar graph arrays for a while now and i've finally got the parts to do it. Problem is being a noob at this stuff i'm not sure my circuit is correct. I've followed the small guides in the forums and rebuilt the circuit 3 times now, but it still don't work!! :cries: For sum reason the leds won't light and if i disconnect the power to the circuit and test each led with a multi-meter led 2 (or 9, depending which way up) doesn't light up. I know the led bar-display is fine because i removed it from the strip board and all 10 led's were fine. If your reading this Macro or Cpemma or anybody....some advice would be great. p.s. How about a complete breakdown of Maplin or Rapid stock codes for all the componants (incase i've got the wrong stuff) Cheers
Welcome to the boards. To troubleshoot: 1) Test that the LED in question is good (sounds like you've done that) 2) check the connection from the IC output to the LED 3) verify that the output pin is 'high' for off and 'low' for on You don't really say which schematic you built, but if its an LM3914 based design, there should be very little to go wrong since there's only about two or three external components. You also don't mention how you are accomplishing your connections. If you're soldering this, I'd check around the area of your 'bad LED' for solder bridges (meaning that you accidentally connected something with solder to something you shouldn't have).
Hi Linear, Troubleshooting done so far:- 1) Led in question does work fine (they all do) but only when disconnected to the stripboard 2) Connection from the IC output to the LED is also good. Checked with a multi-meter. 3) Not quite sure what you mean (being dense about all of this) By the way, Im soldering the whole circuit onto stripboard as Cpemma has shown in the electronics forum (post :- A bit of help with a circuit) Components are:- 10k preset pot (rapid electronics code 67-0230) 10 segment bar-graph display (rapid electronics code 55-0190) 0.47uf cap (maplin code ww58n) 2.2uf cap (maplin code ww62s) LM3914n driver chip (rapid electronics code 82-0712) 1.2k resistor (maplin code M1k2) BTW, I've also checked for bad solder joints ALOT Everything seems to look fine but somehow it aint:cries: I bought quite a few of each component to allow for my stupidity Any advice?
get your meter and measure the voltage at the output pin in question (with respect to ground). You should see a high voltage for an OFF LED and a low voltage for an ON state. Measuring with the LED in place, I would expect you not to see this. But if you disconnect the LED, and you see the proper levels here, we can know that it's a connection problem since you've verified the LED is working properly.
sorry, here is the schematic im using :- http://forums.bit-tech.net/showthread.php?s=&threadid=6949 The diagrams i'm using are, Macroman's edited schematic with the 10k preset included. Cpemma's stripboard schematic and reference table. There all on the forum.
Can't see any errors on the stripboard layout, and the schematic is very similar to the datasheet version. You do have the single track break in line with the preset wiper? The datasheet stresses the need for tantalum caps, or higher value if you use aluminium (say 10uF instead of the 2.2uF). (edit - checked your component codes, all OK)
Hi Cpemma, I've got the single track break in line with the preset wiper sorted (just as your stripboard guide shows). The capacitors i'm using are both TANTALUM bead ones. You can see them here at maplin electronics (codes included) Tantulam 0.47uf code:- WW58N Tantulam 2.2uf code:- WW62S If these capacitors are not suitable can you tell me which are the correct type and values i need (stock codes would be very helpful) What about the polarity of both capacitors, Do i need to connect them in a certain direction???? If so how can i tell which is the correct way Also where on your stripboard pic do you connect to a LM317 based fan circuit.
On the tantalums you'll see a tiny + sign, that must go towards the positive supply, ie, to pin 5 and pin 9. A red and black lead from the bargraph board go to fan (or 317 controller) red & black. Can't see anything wrong with your component list.
Thanks M8 I assume you mean fan+ and 0v (column 1, row 7 and column 1 row 9 respectively as in your stripboard diagram) Are points 1 to 10 on the far right of the circuit connected to 0v of the LEDS as i have done. Not sure why there are two +12 points though....is the second one for the power to the leds? BTW Thanks for checking the component list I'll give it another go this weekend and let you know what i am doing wrong......or...... after all this help, what i'm still doing wrong
