Document last modified December 2005
I am no longer supplying the 'basic bulb firer' component kit for a 'capacitor-discharge' firer. My present recommendation - as a stop-gap measure, until I finish the High Performance Bulb Firer - is not to use a bulb firer at all. If you use a fresh 9V PP3 battery you can fire bulbs directly with few problems. This works better with some designs of slave units than others (e.g. my early slaves and, by some accounts, the commercial Firefly are not always reliable in this respect). My latest versions (PCB numbers SLV011 and SLV021) are designed to fire flashbulbs directly. The SLV021 board also has the option of a built-in resettable fuse to avoid accidental damage to the slave by, for example, connecting it directly across the firing battery by mistake.
To check whether the fuse is included in your unit, look by the large orange capacitor. If there's a small yellow component fitted very close to this then the unit has this self-protection fitted. If the component is not there, just be careful with the way you wire up the flashbulb in the dark. (Some of my ready-built units might have the thermal fuse attached to the terminal block)
To fire flashbulbs directly you simply follow the diagram below. Of course, there's nothing new in this approach - except the important factor which is that my slave unit is designed to be suitably robust when used like this.
There are two potential disadvantages with this circuit. Firstly, you need a fresh(ish) battery, of suitable 'power', so a small 12V car alarm (key fob) battery will not do. And secondly, this arrangement is not suitable for 'flip-flashes' or other arrays of flashbulbs where the bulbs are coupled together with thermal fuses. You can, if you like, add a bulb seated indication to this circuit. You just need to connect an LED and a suitable series resistor across the slave unit. (But then you must get the polarity of the battery correct).
for information about sockets for flashbulbs...
Gibson, David (2001), Flashbulb Sockets, CREGJ 46, pp28-29, Dec. 2001.
Ask me and I'll get around to putting a PDF on this site.
For a while now I have been hoping to be able to supply a new version of my slave unit with a built-in bulb-firer, so that you can fire flashbulbs without the problems associated with using slave units with conventional bulb-firers. Having tried various options, I now think that a combined firer and slave unit is not necessarily the best way of approaching the problem. so, instead, I have begun to think about producing a bulb-firer unit that plugs into my slave unit, as an 'add on' feature. This project has been delayed for rather a long time and at present (2005) I have no immediate plans to return to it and it is not completed. You can read about progress here...
Gibson, David (2004),
A High-Performance Flashbulb
Firer - part 2, Cave Radio & Electronics Group Journal
55, pp22-23, March 2004
Flashbulbs are
still the professionals' choice for cave photography. This project by David
Gibson - which is an update to his article in CREG journal 45 (Sept. 2001) -
describes a compact, microprocessor-controlled bulb-firer that includes
'seated' and 'fired' indicators and a boost circuit to produce 24V from the 3V
supply.