Hello.
Being relatively lazy and constantly lacking time for experiments, but wanting to use those IV-6 VFD's bought at Friedrichshafen fair last June, I studied a way to adapt a cheap LED clock kit to 7-segment tubes.
I have documented my first steps towards a functional VFD clock on my blog (
http://ik1zyw.blogspot.it/2015/09/transforming-7-segment-led-clock-into.html). Since the clock board uses common anode LED displays and active low segments, I designed an adapter board around ULN2003 to pull-up the voltage and invert the control signal towards anodes and grids.
I am having troubles finding a correct value for the pullup resistor on the outouts of ULM2003, so I ask if anyone has been driving VFDs (specifically IV's) with an ULN2003 and which resistor has been found to be optimal. In my experiment, 3k3 is fine but means too much power is dissipated in each R (250 mW or so at 30 V), at 51k some segments don't turn off. The truth lies in between for sure, but a hint will be greatly appreciated since I have already soldered the 51k .... Grids have a lower pull-up resistor since they do draw some current.
Meanwhile I have received a second version of the clock board which includes dimming and a temperature sensor. It even has a relay output! Relay component not included in the kit.
