On 11/19/2013 1:36 PM, John Rehwinkel wrote:
I want to build a four digit VFD clock (three of them actually) without using
drivers like the max6921. I have two possibilities at this moment, one is this
http://i.imgur.com/D4FGaV1.jpg
and the other being this one http://i.imgur.com/5fMc7ty.png .
Which would be best?
I'd use the more traditional design with a resistor in series with the base of
the NPN transistor driven by the CPU, rather than the emitter resistor as you
showed.
More or less like this:
http://www.dos4ever.com/nixie1/multiplexing.gif
That resistor R5 from base to emitter of the PNP transistor can be a lot lower
value, as low as R6/Vanode. It will make the anode turn off faster, the lower
resistance it is.
The transistors can be any type rated for more than the VFD anode supply.
Also, if your VFD is too bright, you can reduce the brightness by reducing the
duty cycle, which is done by turning off the anodes on for some time in each cycle.
--
David Forbes, Tucson, AZ
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