I am building a home beer brewing rig that has several electrically actuated components controlled by an Arduino.

The typical scheme is Arduino -> Shift Register -> Relay -> Component.

One of the components is an electrical BBQ igniter. The problem is that when I turn it on, the shift registers go all wonky and randomly turn their outputs on and off with every spark.

I realize that the main problem is that the igniter is being energized by the same power supply as the rest of the system and that it creates a power surge when it generates a spark. But, how do I neutralize that problem?

One idea I had was to put a capacitor across the igniter input. That didn't help. My analog circuit knowledge is not so awesome.

Anybody have any ideas? Much appreciated.

P.S. The shift registers are 74HC595.

  • 1
    \$\begingroup\$ I'm a bit worried about an automated system that is responsible for ignition. Automated gas operated appliances have a flame safety device to shut off the gas if it's flowing with no flame present. Omitting such a feature poses the risk of gas accumulating and causing a fire or explosion. This could happen if the flame is blown out, or if software or hardware failure causes the system to flow gas without igniting it. Grills get away without one because they are operated attended and outdoors. I'm not trying to discourage you from your project, but safety is important. \$\endgroup\$
    – Theran
    Commented Oct 23, 2012 at 5:28
  • \$\begingroup\$ A schematic would be useful. Try on of the many online where you just draw and share the link. Someone will help you with in lining the image into the question. \$\endgroup\$ Commented Oct 23, 2012 at 5:46
  • \$\begingroup\$ You need to decouple with a capacitor as close to the igniter as possible, maybe run the wiring a couple of times through a ferrite core, but your problem has very likely to do with the electromagnetic interference from the spark itself. If you power the ignitor from a separate power source, is the electronics more reliable then? \$\endgroup\$
    – jippie
    Commented Oct 23, 2012 at 6:12
  • \$\begingroup\$ Would it not be better to use a high-speed igniter used like in gas boilers for hot water/home heating. Im sure if you look how they use it, with some wiring you will find your solution. Newer ones also use MCU's to control the system. A BBQ lighter?I cannot even begin to imagine how you wired that up? \$\endgroup\$
    – Piotr Kula
    Commented Oct 23, 2012 at 14:33
  • \$\begingroup\$ Here's my noobtastic circuit. circuitlab.com/circuit/t6nqm6/igniter-control Yes, safety is a huge concern, and like a grill, it will be outside and attended. \$\endgroup\$
    – Josh Jones
    Commented Oct 23, 2012 at 16:40

1 Answer 1


The capacitors should go across the power supply terminals of the various components like the shift register and igniter, to bypass noise riding on top of the power. When noise comes from some other device, the capacitor can help shunt it to ground. Reciprocally, when a sudden, brief current demand comes from the local device near that capacitor, the capacitor supplies the demand, so that there is less of an effect on distant parts of the circuit.

For better answers, you might want to show the exact circuit diagram, including power supply details.

  • \$\begingroup\$ Good advice. How do I determine the specs for the capacitor to use? I assume it's best to know something about the noise that is occurring, but I'm not really sure how to figure that out. \$\endgroup\$
    – Josh Jones
    Commented Oct 24, 2012 at 3:01

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