older Serial port stamp board
henrytj
Posts: 90
Years ago I bought a basic stamp kit of some sort at a Radio Shack store that was closing shop. I know the board was a serial port connection type, but don't recall much more about it. I was starting to experiment with it on my old computer, which hasn't started up in a while. Now, I'm considering revisiting a project that I was working toward back then of having a digital camera triggering a series of flash units in a pattern. But, that basic stamp purchase is in a box somewhere. Going to look for it soon. Here are some issues I will ask together.
1. The newer Win laptop that I am currently using lacks a serial port. I have seen indications that some USB to Serial connectors might work. So that is the first problem to overcome once I find what box all my electronics stuff is in.
2. Some flash units (like one I have) have a relatively high voltage (as in 100v) trigger circuit. (despite being a battery powered flash unit.) Anyway, at the time years ago, I was reseaching ways to isolate that trigger circuit from the Basic Stamp which could be damaged. I was tryinng to find either a high voltage transister, an "opto coupler", or even an RF solution.
3. In writing a loop to keep looking for the incoming flash sync trigger signal from the camera, I was wondering if I should have a wait/delay command (not sure what it's called as the manual are in the box with the electronics) or if the loop can just cycle as fast as possible. Does that use up the battery faster, or maybe overheat the processor? The Stamp needs to react fast, like within 1/100 of a second after detecting the camera flash sync. then set off one flash, wait a couple milliseconds, set off another flash, etc. The idea is to photograph a dancer leaping into the air.
I almost had this worked out years ago, when life happened and I put it all away. Now that I'm unemployed (yet again) I'm thinking of revisiting this project. (though someone who had borrowed my flash units returned them with some of them no longer working. Oh well, *shurg*)
Anyway, sorry about the too many questions.
Henry
1. The newer Win laptop that I am currently using lacks a serial port. I have seen indications that some USB to Serial connectors might work. So that is the first problem to overcome once I find what box all my electronics stuff is in.
2. Some flash units (like one I have) have a relatively high voltage (as in 100v) trigger circuit. (despite being a battery powered flash unit.) Anyway, at the time years ago, I was reseaching ways to isolate that trigger circuit from the Basic Stamp which could be damaged. I was tryinng to find either a high voltage transister, an "opto coupler", or even an RF solution.
3. In writing a loop to keep looking for the incoming flash sync trigger signal from the camera, I was wondering if I should have a wait/delay command (not sure what it's called as the manual are in the box with the electronics) or if the loop can just cycle as fast as possible. Does that use up the battery faster, or maybe overheat the processor? The Stamp needs to react fast, like within 1/100 of a second after detecting the camera flash sync. then set off one flash, wait a couple milliseconds, set off another flash, etc. The idea is to photograph a dancer leaping into the air.
I almost had this worked out years ago, when life happened and I put it all away. Now that I'm unemployed (yet again) I'm thinking of revisiting this project. (though someone who had borrowed my flash units returned them with some of them no longer working. Oh well, *shurg*)
Anyway, sorry about the too many questions.
Henry
Comments
Your question #1 can be answered with the following:
http://www.parallax.com/Store/Accessories/CablesConverters/tabid/166/CategoryID/40/List/0/SortField/0/Level/a/ProductID/378/Default.aspx
As for the other 2 questions, I'm sure the resident forum wizards will help out.
If you are going to have to purchase a serial adapter I'd seriously advise considering getting a QuickStart Propeller board instead. It's about the price of a USB-serial adapter, includes its own USB-serial adapter, and is also a much more powerful controller than any of the Basic Stamps. If you're going back to the drawing board anyway you might as well go to one that will take you further.
On the isolation thing, you need to figure out what the sense voltage is on the flash trigger pin. That's what you probably have to short out to trigger the flash. I'd be surprised if it's really 100V, most flashes have a transistor driver to create the pulse for the flash trigger coil. If it is indeed high voltage then there are cheap bipolar transistors which you can wire up common-collector style to do the voltage shorting trick from the logic level drive of a Paralax uC. You could also use reed relays; our resident Erco has linked to several eBay auctions of cheap relays that even though rated for 5V work fine off of the 3v3 Propeller I/O pins and can be directly driven by the uC.
About the flash units. I have 3 identcily ones, very old (like from the 1980s) and their sync voltages, as measured with a multimeter, are 15v. These are wall outlet powered units.
I also have an off-brand battery powered unit, and yes, when measured with a multimeter, the sync connection reads as 50v-100v. I stopped using that one after I had measured it.
Yes, the sync connection holds a voltage, and when the contact is closed, the flash fires. I used to have an old view camera (the kind with the accordion-like section between the lens and film, and you had to hide under a cloth to focus it. Purely mechanical, and it was the only one I used the one battery flash unit with once I saw how high the voltage was on its flash sync connection.
Question? Will relay work fast enough? Looked at the specs on my current (and older) Canon DSLR, and it can sync at 1/250s. Might be needed to photograph a dancer leaping through the air if there is too much ambient light. Can the Stamp or Propeller operate that fast, in like 1/500s, to sense the sync from the camera and send out several sync signals to several flash units several milliseconds apart? Anyway, need to experiment when I find everything. Actually, now that I rethink it already, I will probably use a one second exposure with flash units going off at fraction of a second intervals to catch the dancer leaping.
Thanks again,
Henry
Anyway, some one had loaned me a USB to Serial adapter and, again, it actually seems to have worked. At least for the "Hello World" echo back program. All this has me worried that its working out too well. This means that when I go to use the Basic Stamp, it's going to explode, or something.
Now I need to start building my camera-flash control box. I couldn't find the "Wait" command that was mentioned, but I did find a "Poll" command. However I don't think it is implemented on my version of the Stamp. So I might be back to using a loop to check for the change in state of an input. I have a bunch of notes, and again will have to try and re-learn transistor basics to figure out which circuit I was going to use to trigger a 15v sync flash unit.
Thus will probably be asking some more annoying questions over the next couple weeks.
Thanks,
Henry.
But now, in looking around I see that another chip ULN2003 has 7 built in drivers that need no extra resistor from the microcontroller, and maybe even on the flash unit side. A couple problems. Radio Shack doesn't seem to carry that exact chip. They have others that seem similar, but they are online order, only. And not quite sure yet how I'd connect them up to the flash unit. Have to study the divice more before I commit. Thing is I don't want to send power to the flash unit sync trigger, but ground it's already energized sync connection like closing a switch. I think it would be easy, but not sure. What if I have different flash units with different sync voltages?
Hopefully I wont fry anything.