Matrix Orbital Corp

Hi all,

I've followed Cheese tutorial in order to create a CLCD digital baybus but it is not working. I've emailed Cheese but there was no answer (Cheese, are u on vacation?)

My problem is the following. According to the tutorial:

when the GPO is 'on' its -VE pin is earthed and no current can flow into the Base (B) of the transistor, so the transistor is off and nothing happens. When the GPO switched off, a small current is drawn from the GPO's -VE pin which is sufficient to fully switch the transistor on.

Well, according to my multimeter, there is always some current flowing from -VE (-1.31 or -2.31 mA when it is off or on, respectively) to gnd. Anyway this does not make any difference on the transistor, since it is always off. The only real difference with the proposed circuit is that I'm using tip31c transistors instead of tip31a (does it make any difference?)


Thanks a lot and best regards / Fernando

What is your model number of the LCD you are using...?

Hi Miles

It's a LK204-25-V (special model for Bit-Tech.net).

Thanks a lot / Fernando

Since the -VE pin is grounded when the GPO is on there should be no current flowing. My suggestion would be to make sure that the GPO's are working correctly before attaching the rest of the cct.

Hi again,

GPOs are working correctly. What I find a little weird is that in the scheme that Cheese posted, it is done like that. Maybe he forgot to connect +ve to -ve? If you connect it, then there should be current flowing to the base, therefore the transistor should be on. I've been thinking on an alternative circuit. I'll post it here in a couple of days to know your oppinion about it.


Best regards / Fernando

Let me know how you make out...!

Strangely enough I'm a busy man, sorry for not replying to individual emails - I rarely find time.

You don't need to use the +VE GPO pin as it's just a constant 5V line...

Make sure you've put your transistors in the right way round (mine are labelled backwards in the diagram as they're pictured from below).

There's nothing wrong with the circuit as I made it, you're using the same transistors right?

Rob.