This is compilation of some of the questions I have been asked over the years.
The Firefly is a commercial product; it comes ready built, with a hot-shoe connector. It is based on my earliest design, but with some small changes. My unit uses a different photo-diode and is more sensitive under-water. In practice you should not notice much difference in the performance. Please note that if you are not skilled in electronics then I do not advise that you try to build my kit. Also, I cannot provide any technical support for the Firefly - it is not my product!
Yes, the opto-isolation of the output from the input makes this possible. The flashgun must operate from 3V unless you are prepared to change some components on the slave unit PCB.
A new battery should give you at least four years of life. If the unit starts to operate intermittently, or seems to be too sensitive then check the battery voltage. It is supposed to be 3.6V. If it is down to 3.4V, it is time for a new one, as it is, for all practical purposes, dead. If it is below 3V then it is definitely time for a new one. The unit will, in fact, operate down to about 2.6V or so with a pair of alkaline batteries, but there is no point to running it that low with a lithium battery.
If you are really worried about this you can fit a switch. But if you really are getting through batteries quickly then either they were not fresh when you bought them, or there is a fault in the circuit. Check that you have fitted C5 the right way round, and measure the voltage across R6 using a high-impedance (e.g. digital) meter. R6 is 3.3k ohm so, if the circuit is using less than 20mA, the voltage across R6 should be less than 66mV.
The line-of-sight triggering range is around 1200m with a gun of GN 30m @ 100ASA - with a smaller gun, the range will be lower. This high sensitivity allows the slave to "see" round corners in dark passages. Suppose the light bounces round a passage, hitting the walls four times. If the walls have a reflectance of 10%, then a calculation shows that the range would drop to only 10m. Cave walls can have a reflectance of less than this. The range will also be reduced if the op-amp is faulty (e.g. progressive damage due to your not taking proper anti-static precautions during assembly; or if the board is damp or dirty. If you use a water-based flux you must scrub it off immediately after soldering.
Although the unit is insensitive to cap-lamp beams, it is not completely insensitive. If you shine a light on it suddenly, or move it to intercept a beam then it will likely fire. A good way to test it is, in fact, to point it at a light source and snap your fingers in front of it. The rapid movement of your finger creates a pulse of light sharp enough to trigger it. But if it does appear to be behaving intermittently then you should suspect that it has got damp. Apart from direct contact with dampness, it seems that some flashguns are particularly sensitive to water in the connectors.
Yes. This new design features a more rugged output stage than previously. (In the past it was possible to damage the unit if you were not careful about how you fired the flashbulbs). You can use a battery to fire the flashbulb directly, or you can use a conventional capacitor discharge circuit. In the latter case, the slave will latch on, and you will need either to unplug it to re-set it, or to briefly press the flashgun's manual firing button, which achieves the same effect.
I do not advise it. It is very easy to make a mess! If you have an electronic soldering iron and some experience of hobby electronics then you should be OK, but this is not a project for beginners. You'd be better off buying a Firefly (Incidentally, I don't get any commission). You can buy a partially-built kit from me if you think that would help. It consists of the populated circuit board - but you find your own connector and box.
Apart from the printed circuit board - which you can get from me - you should be able to get the other components from a professional electronics supplier. Some of the parts might not be available from a high-street 'hobby' electronics shop. If you live outside Europe then you might have trouble identifying some of the part numbers. Some electronics knowledge will help here.
No. My kit of parts has been provided purely as a service to experienced electronics constructors because some are difficult to obtain. If any components are faulty then they will be replaced free of charge, but this offer does not extend to fixing or replacing built or partially built units. If you wanted 'after-sales service' then you would need to pay more, or buy a finished product - I do not make any profit out of selling these kits.
RALF stands for "redundant array of little flashguns". The concept was invented by Mike Bedford as a way of preventing flashgun failure. I used to provide a slightly larger PCB, which had room for extra components to implement the additional features. If you omitted the extra components, the unit was similar to the basic slave unit. The extra features were not necessary for its operation and they did not make it 'better' as a slave unit - they just allowed you do extra things with it. For example, you could program a delay so that the unit did not trigger instantly. This could help to avoid contentions between automatic exposure flashguns, and with an array of slaves all set to a different delay, you could 'smear' a moving cascade of water instead of freezing it into little drops, as a single electronic gun would do.
I no longer supply the RALF PCB, but a programmable delayed fire is available on the new digital slave unit.
Many digital cameras have a brief pre-flash to set white balance before the main flash. The slave unit would therefore need to trigger on the 2nd flash pulse so, as it stands, the slave unit will not work with such cameras. A similar situation occurs with a red-eye reduction facility. The new digital slave unit can be programmed to ignore flash pulses that occur before the main flash.