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Support Forum » What am I doing wrong??

December 04, 2010
by Ralphxyz
Ralphxyz's Avatar

I am "trying" to set up a new NerdKit.

When in program mode I get 1+1/2 black bars for 30 seconds and then a empty LCD. In run mode I get some random marks and then empty LCD.

I cannot program or run programs.

If I put the mcu into another NerdKit it runs and programs as expected so it has to be something I am doing!


It will be embarrassing but I sure hope someone can see what I have done wrong.



December 04, 2010
by hevans
(NerdKits Staff)

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Hi Ralph,

It is not very clear from your picture, but I think pin 11 of your LCD might be heading into the wrong MCU pin. It is supposed to go into MCU pin 4 (unless you changed the LCD code), and from the picture it looks like it's going into pin 2.


December 04, 2010
by Ralphxyz
Ralphxyz's Avatar

Nope bad angle. Pin 11 to Pin4

Here is another angle of a new breadboard with the same results. New

I thought possible I had blown the breadboard but I am getting the exact same results with the new one.

I have rewired this 6 or 7 times, all with the same results.


December 04, 2010
by Rick_S
Rick_S's Avatar


What are you using to power the kit? If it's an AC-DC power block, you might try adding some filter caps. I don't even see the .1uf at the power pins of the micro.


December 04, 2010
by BobaMosfet
BobaMosfet's Avatar


You've got to do a little debugging on this. Use your voltmeter (it is your best friend!). Try this:

  • Put voltmeter across positive and negative rail and then turn your kit on- what does the voltage do? If it sags, or drops, you either have a short (or your battery needs replaced; or your power-supply is bad).
  • Test voltage same as first point above, both before and after the LM7805.
  • If voltage is 5V downleg of the LM7805, is it the same -everywhere-??? what do you see at the aRef pin? What about pin 1?
  • Check your pin-14 setup- is there a problem there?
  • LEDs are your friends. Put an LED and appropriate resistor on each of the TX and RX pins (2 & 3), so that you can see what activity is occurring when you try to write to the MCU. 160 Ohms should work.
  • Put your voltmeter across the positive and negative leads of the display- how much voltage is being dropped across it, and what happens during the power-up, run, go-wonky sequence?

Information is key. I don't know if you have an o-scope, but now is a wonderful time to really learn how to use it, if you have one.

Please let us know what you find with your voltmeter! :D



December 05, 2010
by Ralphxyz
Ralphxyz's Avatar

I am using a Dell PDA 15 V 2.0 amp brick power supply which I assume would have a filtered supply.

But good eye Rick I had missed the bypass capacitor on that new setup, I have since added it with no difference.

Here are my multi-meter readings with comparisons to a working NerdKit (I have two working Nerdkits but I want to start on the LED-Array project so wanted a dedicated breadboard).

pwr in 7805 15.21 v.
7805 pwr out 4.91-4.92 v.
pin 1 4.92 v(?)
pin 7 4.92 v
pin 20-21 4.91 v.
pin 14 has spdt switch to Gnd (up to ground down open, NerdKit terminology)

How would I see a voltage drop across the display? I just see rail voltage. Would I have to put the meter in line like to see amperage or I added a 1k resistor in line with the Gnd coming from the LCD and see 1.45 v. Is that what I should see?

Working Nerdkit readings:

pwr in 7805 15.18 v.
7805 pwr out 4.93-4.94 v.
pin 1 4.93 v(?)
pin 7 4.93 v
pin 20-21 4.93 v.
pin 14 has spdt switch to Gnd (up to ground down open)

Looks the same.


December 05, 2010
by esoderberg
esoderberg's Avatar


On the second picture, I don't see a connection between SPDT switch and ground.


December 05, 2010
by Ralphxyz
Ralphxyz's Avatar

Yeah Eric that was because there wasn't one, duh good eyes.

I rushed that setup and didn't do normal things and still got the same results.

In fact my bread board requires a jumper in the middle of the rails on both sides which I didn't have so I also was not feeding VCC directly to pin 7 or pin one which I discovered thanks to BobbaMosfet exhortation to test everything with my multi meter.

Even without the capacitor, switched pin 14 or direct power to pin 7 I was getting the same results as on a good NerdKit breadboard.

It appears I have a bad LCD display as I can program the mcu with a LED Blink program and it runs correctly!!

I have removed the LCD wiring so I am loading the program blind but the program is loading I have loaded a couple of different programs on different devices and they all run!

So I think I am good to go, now I can start on the Led-Array project.

Thanks everyone for the help.


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