The talons are simply two wires with a piece of nichrome wire attached between them inside a convenient clip, so they do function as a resistor. I have never measure these myself, but I could get some resistance measurements off of them (I will do that and post the results). The recommended firing current for the talons is 1 to 1.5 Amps. The ematch that I use sometimes (I use talons mostly) have a nominal resistance of 1 +/- 0.2 ohms with a recommended firing current of 1 Amp per the manufacturer (I will check the resistance of some of these as well).What, electrically, are the devices attached to this thing? Are they blasting caps, or strips of nichrome wire that look like resistors, or something else that looks like resistors, or capacitors, or what? Also, clearly 25 mA is not enough to set them off, and someone thinks 3-6A might be needed. Do you have any experience or numbers. Designing an output stage, even one that is a saturated switch, is better when the load is known.
Back to the manufacturer, now that we know what he sends out as a test, the next question is what he needs to see to conclude that the test was successful. In other words, is he looking for some minimum voltage developed across the load to proclaim that a load is connected? If so, what voltage? There are several ways to emulate a load device to keep his system happy, and the more I know about stuff the easier and more reliable it will be.
The schematics are based on a go-to part for some counter circuits because it is counter and decoder all in one. But as you can see, expanding it beyond its natural 10 count limit gets a bit messy. That's why I'm working on a non-4017 version.
For what it's worth, most of the controllers I have seen have been designed for a maximum of 10A. This may be due to the ematch with the lower resistance pops almost instantaneously (~250ms or less). See the videos below for a demonstration:18 V / 1.2Ω = 15 A. So the devices basically are fuses that are intentionally blown? If so, then the output switch device needs to be able to handle whatever the transient current capability is for the 2 second pulse. Not a problem, just a fatter MOSFET.
A 25 mA current through a 34.8 ohm resistor makes 0.9 V. So to convince the controller that this line has a valid load, we need to sink 25 mA at a compliance of about 1 V. Shouldn't be too hard. Is there some kind of spec or general industry practice that establishes a range for a valid device cold resistance?
Does the operating panel have to be waterproof? Or is the lid open only to make connections, then closed throughout the show?
I have to get them out of storage (it's about time to anyway). I should be able to post my findings tomorrow afternoon.Pictures...!!! The FET part number tells us if it is n- or p-channel, an important detail. Also, while the standard power MOSFET gate voltage range goes to 20 V, most CMOS logic quits at 15 V or 18 V. This raises a subtle question about their control circuits. Pictures...!!!
Don't get too excited about a 10 A part. Power MOSFETs started to take over mainstream switching power supply design in the early 80's. 30 years later, parts with *less than* 0.001 ohm Rdson are cheap:
Toshiba TPHR8504, 40 V, 150 A (continuous), 0.85 milliohm (!!!) - - $2.55, single piece.
Wow, that's great! Scott is a really good guy to deal with. I sent some pics your way. Let me know if you want anything different.I called and talked with Scott. He switches both the high and low sides. The high sides are switched individually with P-channel MOSFETs. I think the low side is a single switch controlled by the ARM key or something like that, but he wasn't exactly clear. He's primarily the software guy, and the circuit was done by "an engineer" who was not available. He doesn't see any problem with us using low side switching, so I'll stick with the n-channel FETs for now.
Even without part-number-clarity, pictures would tell me a lot about the nature of their design.
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by Luke James
by Luke James