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Build your own flash slave sensor for less than $5

Rolland Elliott , Jan 08, 2001; 02:09 p.m.

Well I thought I would build my own flash slave sensor for less than $5 when I bought the book "Electronic Projects For Photographers" by Walt Bregach, pub by TAB Books Inc. IN 1983. ISBN 0-8306-0144-9 Chapter 8, page 164.

The only electrical components necessary are a LASCR (light activiated silicon controll recitifer) and a resistor. The book suggests using a Motorolla MRD 920 LASCR with a 27K ohm resistor OR a Radio Shack LASCR part # 276-1095.

Unfortunately I searched the web for about an hour and couldn't find any electronics place that sold LASCR's. Anyone know of a source?The book recommends a 200V, 1amp LASCR. Higher voltage is OK.

There was a past discussion on this topic at: http://www.photo.net/bboard/q-and-a-fetch-msg.tcl? msg_id=000kyA&topic_id=23&topic=photo%2enet but that message doesn't have the info I need.

The closes I came to finding this part was going to: http://store.yahoo.com/webtronics/index.html And using the search engine looking for plain SCR. They have SCR's but I don't think they have LASCR's

Building the slave is darn simple. Just attatch the anode of the LASCR to the positive terminal. Attatch one end of the resistor to the gate of the LASCR and the other end of the resistor along with the cathode of the LASCR to the negative terminal. That's it!

Now if I could just find a LASCR! Peace, Rolland


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Daniel Taylor , Jan 08, 2001; 03:11 p.m.

you can buy these flash triggers for $5-10, which includes casing and PC connector. not sure what you value your time at, but this seems like a poor plan.

Tony Zipple , Jan 08, 2001; 05:55 p.m.

I doubt that it is very cost effective to spend the time and money that you are taking, but it sounds like a great learning experience. But I know that when I tackle things like this the value is in the knowledge that it generates more than in the final product which often costs more and works less predictable than an off the shelf substitute. I heard the same thing from a friend that built a workable, though clumsy, studio strobe. Good luck!

Bill C , Jan 08, 2001; 07:10 p.m.

Roland, this gadget builder book (1997): (link)

has a slave trigger on pages 140-141. It uses a photo-transistor (L14C1) plus an SCR (C106D or C205D) for the guts. Presumably the parts are available.

I was also concerned about the value of your time; however, on further thought it would likely be as cost effective as my time on photonet, so I won't say anything further. BTW, if you're interested and can't find the book, I could copy the schematic/parts list.

Michael Werner , Jan 08, 2001; 09:14 p.m.

Daniel or anyone, Where do you get these for $5-10 and what exactly would we be looking for? I checked out B&H, but there are a bunch of products and I'm not sure which is the bare minimum needed to make a slave flash out of an on camera (but not built in) flash.

Todd Frederick , Jan 08, 2001; 09:14 p.m.

Daniel...where can you buy slaves for $5 or $10. The going rates seems to be around $35 from Wein. Please share your secret. Thanks

Michael Werner , Jan 08, 2001; 10:19 p.m.

Is this what's being talking about?

Click Me

Daniel Taylor , Jan 09, 2001; 01:00 a.m.

yes. that is an elaborate version, the ones that I see new and used have a single PC connector and resin body. there are off-brands that I have seen in my travels for quite cheap.

Wein makes a very nice one, much like the Hama, with a hot-shoe and PC connector. the problem, is that the way they milled out the hot-shoe, the top plate of the shoe is too fat to allow a Canon 550EX flash to fit. the bottom is not solid plating like most, allowing the control pins to float and not short together.

at swap meets I will pick up several *peanuts* for a buck or two, so building one holds little intrigue for me. could be thirty years of electrical engineering and breathing too much flux fumes doused my enthusiasm too.

David Doyle , Jan 09, 2001; 02:17 a.m.

$29.95, sign me up! I'll be the first to tell you Rolland that you'd be wasting your time building these things (unless as previously mentioned-that it would be a learning exp.). Think of all the time you could be out improving your flash technique instead of saving 25 samolians (well plus shipping and handling). If you are into saving money, consider winding your own film cans and developing your film yourself.


One who has breathed plenty of solder fumes.

Wayne Walker (UK) , Jan 09, 2001; 04:14 a.m.

I have used Jessops (www.jessops.com) versions of these units on Canon 430 and 550 flash guns very successfully, for taking shots of Dolls, still life and for a small portrait studio set up. They cost £9.99 code - JESMSU. www.maplin.co.uk may have the components

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