Tiny VFD clock

[Mad_Hank]

Okay after debating some exotic clock on a chip solutions from the VFD era I decided to go for my original idea.
I will edit this guys source code because I'm not that much of a software guy; http://thecustomgeek.com/2011/06/29/multiplexing-for-a-7-year-old/
I will probably use LM2596 powersupplies off ebay for the V+ because I hear from more and more people that VFD displays at their recommended voltages are way too bright. ***
VFD's have been upgraded to IV-11 tubes because I have more room than expected.

*** just noticed that these are step down only

[Mad_Hank]

NPNs aren't connected right... looks like you couldn't decide if you wanted common base or common emitter

I just realized what you mean!

Where I connected my ground I should have connected my uC pin, and where I connected the uC pin I should have connected the 5 volt supply.

But I posted this on another forum and people over there said that my (mistake) should work.

Well I can order the parts anyway since that is merely a layout thing.

[Mad_Hank]

Yikes I just bumped into another problem:

0.0035/25*3 = 0.00042
60/0.00042 = 140k = 130K or 150K ohm

suppose I lower my voltage to 40 volts because the tubes are very bright:

40/0.00042 = 100k

that is a deviation of 40-50%

I ordered both values but how will this affect my final design.

[edavid]

Yikes I just bumped into another problem:

0.0035/25*3 = 0.00042
60/0.00042 = 140k = 130K or 150K ohm

suppose I lower my voltage to 40 volts because the tubes are very bright:

40/0.00042 = 100k

that is a deviation of 40-50%

I ordered both values but how will this affect my final design.

The resistors supply base current... lower voltage -> lower VFD current -> lower collector current -> lower base current.  So, no problem.

[codeboy2k]

even though people on the other forum said your mistake should work, it's much, much better off as a cascode (common base input) as edavid suggested. If you still have the time, you should correct it and configure it as a common base input cascode, i.e. bases to +5V and control input is via the emitter.

The cascode has much higher isolation from input to output and thus offers much better protection for the microcontroller from the 60V high-voltage supply.  I'm surprised no one has mentioned this yet.  Also, the cascode won't suffer from base leakage that might turn it slightly on, as would be the case with the common emitter (your drawing mistake). i.e. tri-states or pullups on the I/O port won't turn it on.

[Mad_Hank]

Okay thank you, I tried applying for a few samples of the HV5812 anyway, but if those are declined I will go for the big box of transistors

And anything can be changed until my soldering iron is cold