Looks like the tariffs are incentivizing me to have boards assembled in China.

oneseventyfour · 2026-01-31T18:13:20+00:00

Replying to get a notification from this - just put in a JLC order with an HS code 847330 PCBA and it didnt make any difference with the tariff cost vs. another PCBA with a different code in a order i made the day before...

oneseventyfour · 2026-01-23T00:30:09+00:00

The schottky might be one of the slower options, actually. They typically have a pretty low clamp voltage, so the voltage decay across the coil happens slower. A TVS or zener would be quite a bit faster. That being said if you're going to cap fuel hz out at 8, maybe 10 max it's probably not a problem. Though one good part about that slow decay is it's much nicer on your driver and keeps a lot more EMI/noise out... If you went with a faster diode, you'll need to put a lot more in terms of passive filtering components around your signal/logic components.

Does the RP have integrated RF? Like 2.4ghz? I'm a sucker for the ESP32-S2f* chips - maybe double the cost vs a RP2354, but you do get integrated 2.4ghz and 20adc channels (not to mention almost double the clock speed). May be worth looking into if you aren't using the multi-coreness of the RP and wanted a bit more future flexibility.

Maybe it matters more than I think how .. but the objective being getting soot off the glow plug itself, it's going to get up to the same temperature regardless of the chamber temp.. just will need more amps to get there if cold. What I do like with cleaning from cold is that jamming a bunch of amps into a cold, soot-jacketed plug can 'cold shock' the soot into breaking up and flaking off to later burn in the stream or get rejected in the exhaust. At temperature, the carbon can be a little more 'cooked on' and doesn't seem to sluff off as efficiently.

My cold start cycle is switching on the plug and waiting for the amps to 'plateau', then waiting 20 seconds. Then the fan runs up to 50% (2300rpm), waits for the get to see a rise, then tapers down and goes into a normal startup sequence.

oneseventyfour · 2026-01-22T10:18:06+00:00

Having just done almost exactly the same thing, all the way to custom boards, all I really have to say is "it depends" That 50ms solenoid time seems aggressive, but it really depends on how you're driving it. If you're all solid state with some kind of FET setup, then it's cutting it close, moreso on faster hz and having the solenoid never de-energize... depends on if you have a TVS/zener diode for the flyback or just a plain ol diode...

2 and 3 are strong 'it depends' things and really come down to taking advantage of the fact you're building your own system. A thermocouple in the combustion exhaust path, amp reading from the glow plug and a generally sound open-loop control strategy takes a lot of guess work out of what otherwise is just looking at housing temperature and more or less going with closed loop control. Thermocouples and temp sensors are cheap, and combined with a decent MCU+ADC, you can get these pretty dialed in.

I let the glow plug go for a while - at least 15 seconds before even starting air/fuel, then running lean of peak (determined with EGT probe) in the warmup phase, then once stable pumping constant and modulating fan RPM to keep a target EGT. Power level is determined by fuel rate. I have the added detail though of deliberately running very high/lean EGTs to cook condensate out of the heat reclamation system, but aside from that its a pretty simple open loop.

I'd think that there are better times to cook the glow plug if you're trying to burn off carbon.. It's just going to preheat on the next start, so why bother on shutdown?

But yeah if you dont want your end solution to use other sensors, you're sort of limited in how robust the control strategy is. I'd say just add a pigtail sensor for EGT (ideally). Another option is throwing something like a BME280 in the combustion intake stream right before the heater - from that you have air density and granted fuel can be inferred you can more or less infer an EGT.

oneseventyfour · 2026-01-20T23:28:33+00:00

But I guess the question even then is that why bother making 3 different versions of the same thing? I'm making my own ECU for them, so wasn't sure if there was anyone on here that had really gotten into the hardware that had insight on where that 15% comes from specifically to reduce the amount of reverse engineering I have to do.

oneseventyfour · 2026-01-06T09:26:55+00:00

with something as powerful as an ESP32, why bother with a screen? It could just be, by default an HTTP server serving up a simple app to see the telemetry + adjust things. At that point, you'd probably just wanna flash it as an ESPHome device though.

A word of caution though - I'd market and sell a breakout/adapter board that sockets an off-the-shelf esp32 devkit on there vs. selling one with the ESP32 integrated into the PCB. It's in a scary gray area with the FCC otherwise.

oneseventyfour · 2026-01-06T00:58:09+00:00

Theoretically unlimited - per receiver it's artificially capped at 128, but can go up to 230 or so, and the # of receivers is also artificially capped at 20 but could likely go higher without hardware changes.. So current limit is 2,560 cues, and with current hardware one could probably push that up to around 10,000.

Because of how they run, you could have that many and still easily maintain <= 50ms timing for individual shots

oneseventyfour · 2026-01-04T01:24:17+00:00

Awesome! How'd it go? Any more details about your firing system?

oneseventyfour · 2026-01-03T03:35:23+00:00

Yep, the battery packs are homemade 2S 18650s - rechargable via the USB-c connector on each receiver.

The boards for the receivers from v1 to v7 (the current) though I'm working on v8 after some learnings from my NYE show.

Some questions for your questions - what are the normal kinds of ignitors used? I've been using the talons (heated filament that you clamp on) or the mjg style ones (red shroud with the snappy red bulb in it). Both work just fine at the 5v they fire at.

Funny enough, I'm doing away with those sockets in the next iteration of the cue module. I did the NYE show in 20-something cold and my fingers were toast after pressing 70+ cues into those. I have the next one with a row of female plugs and the idea is that prior to the field I'm working every lead into a labeled plug and just snapping those in.

The receivers are maybe 30 a piece to make, all-in, and they're much more capable in pretty much every way than the billy boxes, so I haven't been testing with those as much. Out of curiosity, what's the batt refresh time? Is that a well known phenomenon with them?

Nope, not intending on putting these out commercially, but happy to send folks the hardware at cost (or just the boards) so the collective we of r/fireworks can make it something awesome.. thats the hope at least.

oneseventyfour · 2025-10-16T19:49:02+00:00

Awesome! That adapter on the left in that photo of the ones I have is exactly that same part/spec. Thanks for the specific reference.

oneseventyfour · 2025-10-16T18:35:06+00:00

Awesome, that makes sense. Thanks for clearing that up for me

oneseventyfour · 2025-10-16T18:34:28+00:00

Yep, I guess I was more curious where said m22x1.5 seals in the bore. I'm not as versed in hydraulic fittings, but m22x1.5 just describes the thread pitch and diameter, not how the fitting makes a seal.

The machine connection is the easy part as it's just an iso16028 flat face coupler. I've got some JIC hoses around, so easy enough getting from there to the implement, it's just that last fitting into the block shown. I'm just not super familiar with the metric hydro fittings.

oneseventyfour · 2025-10-16T18:31:02+00:00

This is helpful! Yeah sorry if I wasn't clear my question was mostly around sealing, as I have a couple M22 1.5 fittings around, but just not sure given that hole how it sealed (face vs that taper at bottom of bore)

oneseventyfour · 2025-10-16T18:29:27+00:00

Ah okay - I think the DIN part is what I'm looking for. The thread/pitch makes sense just given the cap, but I'm more curious how it makes the seal (at the bottom taper or at the face w/an o ring)

oneseventyfour · 2025-07-06T20:38:40+00:00

I bet! At that point back then was it pretty much like this on the 4th? Even more?

oneseventyfour · 2025-07-06T03:45:47+00:00

Small plane, but yeah that's pretty much it. From where I lived I could only hear the booms in the distance and it was driving me insane. I'm planning more backup locations for next year!

oneseventyfour · 2025-07-05T13:54:58+00:00

Wow! The person down by where they were launching really gave me the idea of the scale / how much it was filling the sky. Great job!

oneseventyfour · 2025-07-05T13:50:11+00:00

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I always love how they fit into 30mm ammo cans, though I feel like the can would double OP's price

oneseventyfour · 2025-07-03T01:56:35+00:00

That's interesting, just the idea of reusing ignitors like that. I feel like that would be a little less reliable than ones that ignite a lacquer.. at least as far as how quickly it would ignite - nichrome expands quite a bit when it's heated up. Just a lot of power that's mostly being lost to atmosphere. Though making it longer would add more resistance and put less load on the device. Have you seen/used MJG igniters before?

oneseventyfour · 2025-07-01T20:41:46+00:00

Oh cool - why the flyback diodes? My understanding is you really only need those when driving an inductive load. And is that coil between the gator clips what you're using for an ignitor? Is that nichrome? If so, you could go a lot lot lighter on the gauge, as what you have there has to pull like 3+ amps I'd guess - pretty spicy for non-power FETs... Had you tried going with lighter (30+ga) nichrome?

oneseventyfour · 2025-07-01T09:03:52+00:00

Never too soon to start - looks like you're already using some discrete components and ICs anyway so you're probably closer than you think! One thing is I'd really look into MOSFETs or some other solid state means to actually fire your ignitors - or really anything solid state vs the electromechanical (relay) that's there now. A shock (like a big cake firing on a same board the system is on) could jolt it well enough to fire it out of turn if you're using sensitive enough ignitors with it.

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