Help - 18m2 Project Board 12v regulated version

jensmith25

Senior Member
Hi all,

I've got a question about the CHI030 project board (18m2) http://www.picaxestore.com/index.php/en_gb/picaxe/project-boards/chi030.html

I am using it with the 5v regulator and a 12v transformer but when I check the outputs with a multimeter I'm only getting 2.44v through the darlington driver buffered outputs.

The direct outputs are reading 12v. Photo below. Only one LED connected for demonstration purposes.

18m2_12vRegulated.jpg

Is it not possible to get 12v through the darlington driver? I'm using it with a potentiometer for speed control of flashing LEDs - there will be 12 LEDs driven from the board so I'd prefer to go through the darlington driver rather than drive from the Picaxe chip directly.

Any info would be appreciated. The instructions seem to indicate you can use the darlington outputs unless I'm misunderstanding it.

Thanks,

Jennifer,
 

hippy

Technical Support
Staff member
The direct outputs are reading 12v.
Those outputs, which look to be the signals from the PICAXE pins, should not be at 12V.

It seems you are running the whole board at 12V. The resistor/link which needs to be removed for dual voltage operation appears to have been removed so perhaps there is something else wrong or I am misunderstanding what you are saying.

If 12V has been applied to the PICAXE chip it may have become permanently damaged.
 

rossko57

Senior Member
Depends how you measure it. You don't "get 12V out" of the darlingtons, their output either floats or gets pulled down to 0V, So with a load connected between 12V and an output, and a meter between output and 0V ; you would see 12V for 'off' (from the 12V supply leaking through the load) and 0V (ish) for 'on'. With the meter across the load, you see the opposite effect.

You shouldn't be seeing 12V at the port B pads if you meter to 0V ?
 

jensmith25

Senior Member
For Hippy: I followed the instructions - cut off the wire link, add the specified 5v regulator and power it via the V2+ power input connector.
Image from instructions: 18M2_12v_Instructions.png

It says the chip should get 5v and the outputs 12v.

EDIT: Just checked from -ve to picaxe and that's 5.1v. The outputs next to the chip read 0v Nothing is hot or smoking so 12v is definitely not being applied to the chip.

Rossko57: I measured between +ve and outputs. Measured between +ve and -ve outputs I got 12v. I'll check -ve to outputs now.

The 12v LED won't light currently when connected and yet when I tested the PCB on 4.5v (without regulator and with the wire link) it was all working fine.

EDIT: Measured between -ve and darlington outputs and they are all 1.5v apart from the one with the LED connected which is now reading 9.8v but still isn't lighting up.

I don't understand why it's not working now when it was running quite happily before I added the regulator and cut off the link.
 
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hippy

Technical Support
Staff member
First thing is to check what voltage the PICAXE is getting; measure the voltage between leg 5 (0V) and leg 14 (+V) of the 18M2. Double check that by measuring between 0V of your power supply and leg 14 (+V) of the 18M2.

Those should both be near 5V. If 12V turn it off, otherwise, download and run the following program -

Code:
#Picaxe 18M2
dirsB = $FF
Do
  pinsB = $00 : Pause 2000
  pinsB = $FF : Pause 2000
Loop
Then measure between the power supply 0V and each of the direct outputs. The meter should show near 5V for a couple of seconds, then near 0V for a couple of seconds.
 

jensmith25

Senior Member
Hippy - Ok, I've done that. Can confirm that it's all reading 5v or near 5v and the direct outputs are reading between 0 and 4.95v ish.

Strangely, my LED is now flashing slowly and the reading off 0V to LED output is from 0 to 10v. All other outputs are reading between 0.6v and 1.8v
 

Goeytex

Senior Member
Make sure that the Anode of the LED is connected to V2+ and that the cathode of LED is connected to the output pin of the Darlington Driver.
 

jensmith25

Senior Member
I just tried re-downloading the original programme to the chip and the LED is flashing away quite happily and changing speed with the potentiometer.

What's going on there????

It's exactly the same programme I had on there before!

Ah well, seems to be ok now. Gremlins presumably. Thanks all for your help.
 

inglewoodpete

Senior Member
Strangely, my LED is now flashing slowly and the reading off 0V to LED output is from 0 to 10v. All other outputs are reading between 0.6v and 1.8v
Jen, Not strange at all. A darlington transistor, with its collector open circuit, will not show much voltage on the collector. Refer to Rosco's post #3.

You will only see a significant voltage on the collector of a darlington when
  1. The collector is pulled high with something and
  2. The darlington is turned off.
 

hippy

Technical Support
Staff member
I find it can help if one thinks of a Darlingon transistor as a relay ...

Code:
                -.-
                 |
PICAXE           `-----(
.----.
|    |           .-----(
|    |----.      |
|    |     ) _ _ o /
`----'     )     o/
         _|_    _|_
That's not entirely accurate for analogue circuitry but is pretty close to how things are when used as a digital switch as it is with a PICAXE output.
 
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