Arduino and Transistors Question - RE: School Musical Production

Hey guys!

I have built one sample circuit on the PCB but I have an issue.

When the wire coming from the Arduino (pin 9) registers 4.95v when it is NOT connected to the board.  When that same wire is connected to my circuit board, it registers 0.9v (from pin 9).

Any ideas what is causing this?  When I built the exact (when I say exact I mean EXACTLY THE SAME) same circuit on the breadboard it works perfectly.

I am missing something?

If you are using the transistor... Maybe you missed the resistor between the arduino output the base of the transistor?

Hope that helps,

Miguel

I'm off to bed but before I do.....

Have you added the 2k2 resistor in series with the Arduino pin to the base of the PN100.?

The resistor is also there to ensure that any stray current from the Arduino will NOT cause the PN100 to conduct.!

As much as your pictures/videos are great, without an idea of which connector does what we are guessing.

It appears that the arduino is connected to the blue? lead standing up between the two blue connectors....however that's an educated guess.

Perhaps you could annotate the drawing with which column/row each connection is ...which would help us to help you.

Mark

It looks like the PN100 emitter on the breadboard is not connected to anything. It looks like the green wire is connected to the base. Is this correct? (if the emitter is not grounded the base could be driven high)

As MCB points out, the NPN PN100 really should have a resistor connected between the base and the arduino because the voltage between base and emitter can not exceed 1  forward diode drop (1 volt according to the datasheet).

just to clarify: the base is NOT connected to anything and the emitter is grounded (as per the schematic posted with the pn100.
The collector is connect to the resistor (r2 - goes to 5v/12v). On the same line is the gate of the mosfet.

the two blue screw terminals are the led breaks that can be seen in the schematic. The one furthest from the mosfet is connect straight to the 5v/12v rail. The other half of the blue connector goes into the mosfet drain. The mosfet source goes to ground.

That should be the same in both circuits.

in the diagram above the base of the transistor is clearly connected to R1 and then the other side of R1 is connected to the Arduino output pin

You need to connect this up for you circuit to work

Wallrug

You may also need to pay attention for dry joints in the final part of this (after you add the base resistor)

These suggest poor contact with the connector.

Your post is very interesting, as I wasn't aware those types of prototype board exist.

For future reference, if you swap the PN100 down to the 'c' row, and place the FET at 'e' row, you could have room for a heatsink.

I always prefer to have them with the metal bit away from the electronics (ie rotated 180 deg), because one day you'll be measuring/adding a wire to the connector when the power is on.....

Then that No5 answer appears   As long as nothing is damaged/destroyed or otherwise had the magic smoke let out.

Mark

edit fixed spelling mistake

Yes Mark those PCBs are quite common I even found some in the Farnell catalogue (did come from Adafruit though!!)

http://uk.farnell.com/mcu-mpu-dsc-dsp-fpga-development-kits_accessories/accessory-type/breadboard-pcb-kit/pg/110514094

Sorry there I don't to Labour it but really  you need to check over that soldering and clean up all those joins  several have far too much solder and several barely any at all and this may just be the problem any number of bad joints would cause your problem

John

John

Thanks for the link .. the small one is for the RPi 'extender' although I used a different type.

mark

I will let the builder know that his work is not up to standard.

Sorry Wallarug wasn't trying to be awful but  bad construction techniques will simply drive you round the twist and if you've copied the breadboard exactly you will be chasing your self until you get past these bits .

Sorry Wallarug wasn't trying to be awful but  bad construction techniques will simply drive you round the twist and if you've copied the breadboard exactly you will be chasing your self until you get past these bits .

I assist with helping students put together an electronic Xmas Tree.

It involves component insertion and soldering some of whom have had some experience, and some none at all.

In each case we try to show them why their solder joint needs rectification, and how to spot a poor joint before firing it up.

The end result of all this (and yours) is a reliable, working well and useful piece of electronics.

In many cases it might work until it is heated and cooled a couple of times, then it only works sometimes.

Hence the reason we are pointing out these problematic areas so that you don't have half a display on opening night.

I'm sure you have learnt a lot from this whole discussion, and this is no more than that ... more learning.

mark

Good point Mark I was avoiding mentioning the inevitable Christmas tree kit trying not to confuse the matter,  but to be fair it's a great excuse to practice basic soldering skills with out the pressure of designing something as well. I have used these with young Nephews and they do indeed like them and get to correct their work as you said...This is the most important thing.. After all those who make no mistakes haven't made anything !

After all those who make no mistakes haven't made anything !

Yep.

The key is trying to spot your mistakes before others...

I'll admit a field of stupid mistakes before now but I keep the photos of them down to a minimum

Ok guys,

All is working.  I had the multimeter in the wrong position of the circuit.

The work on the PCB is of high quality (according to the individual who built it) and I really any help on this project.

I will get back to you when the board is fully built and tested (correctly )

Thank you again.  I'll keep you posted.

wallrug.

Please tell us you now have a resistor in series with the Arduino pin and the base of the PN100.

Mark

nope.

I might investigate how to do this by modifying a few cables with a resistor in them.

I ran out of space on PCB for base resistor.  (30 / 6 = 5 outputs) - an extra resistor would mean an extra hole used.

What did seem like a good idea, suggested by one of you, is that you break the connection on the PCB to allow the resistor to be in the circuit (a bit confusing I know).  The only issue with that is it may crack the whole board. 

Any other ideas to get base transistor on PCB without occupying more space and without damaging PCB too much?

Here are a couple of suggestions:

1) Replace the PN100 with an N channel FET - preferably with a logic level threshold...

2) Program the 2 states of the CPU "output" pin as follows:

1. Output ON (LED Off) - configure the pin as an input with internal pull-up resistor - this will turn the NPN transistor on without stressing the CPU pin
2. Output OFF (LED On) - configure the pin as an output that is always set low (a riskier solution is to leave the pin as an input but with no internal pull-up)

wallrug

I cannot support the suggestion of making it an input, because you can't drive it.

I would remove the two pin jumper you have and insert one end of the resistor in its place. Cut the wire and attach the cut end to the other end of the resistor.

The second option is add it underneath and use the unused side of the board ie row f - j.

mark

I fail to understand why "you can't drive it" - please elaborate.

If the hardware is left as-is and the "drive" pin is simply programmed as an input instead of an output, then:

• when digitalWrite(pin, HIGH) is executed the pin gets an internal pull-up resistor which turns on the PN100 - this command is already in the code and does not need to change
• when digitalWrite(pin, LOW) is executed the pull-up resistor is removed and the pin is "floating" - this does not supply enough current to the PN100 to turn it on, so it turns off.  - this command is also already in the code and does not need to change.

Nothing in the code or hardware needs to change except one word to change the pin configuration statement from output to input:

pinMode(pin, INPUT)