Nixies, power and the DS1307

Hello guys. I am currently working on a nixie clock and I have hit a snag that you may be able to help me with. I am getting the time from a DS1307 using the standard wire library, which works fine until the high voltage to the nixies is powered up whereupon it returns seemingly random values most of the time. As far as I can tell, the power supply is stable though my diagnostic equipment is limited to a basic multimeter. I am running a fairly typical 555 based switch mode supply for the nixies and a 5v regulator for the rest all from a 9v supply with the reset pin of the 555 controlled by the arduino. If I drop this pin low before getting the time from the DS1307 then bringing it high again after, the values it returns are correct but there is some very distracting flickering in the nixies on cathodes that should not be lit every time the power pulses. All grounds are connected, which I am guessing could be part of the problem, because otherwise to get to the DS1307 an interfering pulse would have to get through the K155id1 drivers, the shift registers and the arduino itself.
Any ideas about either how to stabilise the values retrieved from the DS1307 while the tubes are powered or how to eliminate the flicker in the tubes when the power is pulsed?
Many thanks.
Marty.

I'm not sure I follow your hardware setup without a schematic. I'd also like to know how you are using the 555, so I can use it to power my Nixie's... ;)

How much current is your supply capable of? Have you measured what the total project is drawing?

I'm using a supply pretty much identical to the one depicted at http://www.ledsales.com.au/kits/nixie_supply.pdf except i'm running a 7805 regulator circuit in tandem with it and i'm sure that it is sufficient to run all the nixies because in test sketches that I have tried they all work fine. It's only when the RTC gets involved that the problem appears. Seems like an interference issue to me rather than power supply instability. The complete setup is as follows: The arduino gets the time from the DS1307, operates three 74HC595 shift registers, which in turn run a bank of six k155id1 driver chips on a seperate board, which then run six in-12b nixies.

Cool project. Show Photos!

I would next add .1 uf bypass capacitors CLOSE to all the shift registers and drivers, and at the voltage regulator and nixie supply outputs. Is there a common ground point? I would run separate grounds to the 9V power supply (-) from Arduino, Voltage regulators, drivers, nixies.

Let us know how it goes...

How would I go about seperating grounds given that everything comes from a single "wall wart" type adaptor and is dropped and boosted from it's original 9v? Wouldn't all grounds have to be linked in some way to the ground of this supply? I'm actually kind of a beginner at electronics, this is my second real project but I tend to go for the trial by fire approach and go for making something big and complex. I haven't touched the business end of that big capacitor while it is charged yet, so I think i'm doing quite well. I have posted some pics in this thread: http://arduino.cc/forum/index.php/topic,75542.0.html maybe it will help give an idea of what I am working with.

You need a ground plane for all the low-voltage circuitry as well as good decoupling perhaps? The high voltage circuitry ground should be joined to the low voltage ground in one place, and the same place as the control signals pass from Arduino to the drivers. Keep high voltage circuitry / PSU away from logic signals.

The crystal for the DS1307 is extremely sensitive to electronic noise BTW, since its oscillator is using less than a microwatt - you need to ensure it is nowhere near any source of noise and is close to its ground-plane, as the per the datasheet for the DS1307

A power supply PWM chip like the UCC3807 would be a better choice for the high voltage supply. Among other things, the feedback amplifier and voltage reference are built in.

You can get RTCs that have the required crystal integrated into the package. Maxim makes several different ones.