MPSA42 driving a Nixie Colon (INS-1)

[randyrob]

Hey Guys,

First of all I'd just like to say what a fantastic Group, plenty of useful info!

I have been working on a Nixie Clock (http://halfluckbot.tumblr.com/)

I would like to make the Microcontroller flash the colon's in between the Hour and Minute Numbers.
(I will be later on using this for Temperature trends - fast flashing for warming up and slow flahsing for cooling down)

anyway I got some MPSA42's of the 'bay and wired them as following ==>

http://www.halfluck.com/source/nixie/MPSA42.jpg

Then uploaded the simple blink sketch to the Microcontroller.

The issue I'm having is the Colon's just stay lit, they don;t actually blink.

Any Ideas?

Cheers Rob.

[John Rehwinkel]

> I would like to make the Microcontroller flash the colon's in between the Hour and Minute Numbers.
> (I will be later on using this for Temperature trends - fast flashing for warming up and slow flahsing for cooling down)
>
> anyway I got some MPSA42's of the 'bay and wired them as following ==>
>
> http://www.halfluck.com/source/nixie/MPSA42.jpg
>
> Then uploaded the simple blink sketch to the Microcontroller.
>
> The issue I'm having is the Colon's just stay lit, they don;t actually blink.

You may have a weak pull-up enabled on your microcontroller, which leaves the transistor on enough
to light the colon. If your microcontroller is an Arduino and you're using pin 13, the LED on the Arduino
could be pulling your transistor on too.

I'd suggest trying a different I/O pin. Another thing you can do if you have an LED lying around is to
replace your 33k resistor with a 1k to 10k resistor and put your LED in series. That way, the LED
should light when you're turning the transistor on. If you see the LED flashing, that means you're
sending current into the transistor. If the colon still stays on, try adding a resistor from the transistor
base to ground to absorb stray current.

Other things you might want to investigate: does the colon stay on if you power off the microcontroller?
If not, it means your transistor is okay, but your microcontroller isn't turning that I/O pin off enough.
How about if you disconnect it from the transistor? If it still stays on, you may have a bad or misconnected
transistor.

- John

[randyrob]

Hello John,

Fantastic Advice - Many Thanks.

Yes it is an Arduino. I have it on Digital Pin 10 & had 13 Blinking too so I could see what was going on.
That definitely gives me some ideas to work with. I will try all of your recommendations and report back.

Cheers Rob.



 

[randyrob]

Hello John,

I put the LED in series like you suggested and it was indeed blinking, so re hooked up the Nixie Tube and it started working fine!

Now that I have one Colon going can I drive another Colon of the same Transistor? or do I need to use another Transistor?
I guess i'm asking which is the best way to do it.

Cheers Rob.

[John Rehwinkel]

> I put the LED in series like you suggested and it was indeed blinking, so re hooked up the Nixie Tube and it started working fine!

Congratulations! I know that's a good feeling.

> Now that I have one Colon going can I drive another Colon of the same Transistor? or do I need to use another Transistor?
> I guess i'm asking which is the best way to do it.

Yeah, should work fine. Give each colon its own resistor and hook both of them to the transistor and it should work fine. The
total current is small enough that the transistor can handle it easily.

- John

[randyrob]

Hey John,

I soldered up the 2 x Colon's onto one Transistor over the weekend and they are working perfectly, many thanks for your advice

Rob.