| Electronics > Projects, Designs, and Technical Stuff |
| JBC-mini - a low cost T245 handle controller |
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| bdivi:
Long time no news :) any update with this project ? |
| poorchava:
It's on hold right now. I've assembled most of the circuit (excluding the thermocouple interface section) and the project has been put on hold due to shitload of commercial work. What's done so far: -power supply is working as it should -uC works and communicates with debugger -led display works and displays garbage as expected (segment connections have been changed since the prototype but code was not updated) -AC switch works after some modification that involved getting rid of PNP transistors that were driving mosfets. Right now mosfets are driven by optocouplers directly. The optocouplers I chose have proven to have too high dark current and small signal PNPs with high hfe would turn on spontaneously -zero detection works after a little 'woops' which involved a double diode in a diode bridge being put onto schematic in reverse direction, and this resulted in sudden disappearance of the diode together with a few milimeters of pcb track. Anyway - it works now. I'm gonna work on it further, but right now I'm sleeping 2-3 hours a day and have no time to work on private projects. |
| dom0:
Do you know what kind of connector they use and if it's available commercially? Could you confirm if the cold junction is indeed in the hand piece (or in the connector)? I'm currently thinking about something similar, since I have most of (the cheap) parts for something similar at hand (power supply, some chopper op amps, and the usual other stuff). But I'd use one of the laptop supplies from my stock (have plenty of 60 and 90 W bricks) for the power part. Heating with DC shouldn't be an issue and saves one switching element plus the opto-couplers and zero-crossing detection stuff. |
| ajb:
The connectors are Hirose RPC1. They're available for a few bucks in single quantities from Mouser. I've had a T245 handle and panel mount connector sitting around for several months for a similar project, just haven't gotten around to doing much of anything with it. Regarding using a DC supply, I've read in other discussions some warnings that using DC can shorten the life of the heater due to electromigration, but I haven't really seen any specifics as to how substantial the loss of lifespan is, or if electromigration is even a concern with the types of heating elements JBC uses. The JBC cartridges are expensive enough that saving two or three cartridge replacements over the lifetime of the base station probably justifies the extra cost of using an AC supply. On the other hand, the cartridge replacements would be a deferred expense... |
| poorchava:
Yep the connectors are available. As for the cold junction compensation, I'm almost sure that there is none in the handpiece, unless they somehow use the handpiece-cartridge connection as a thermocouple (I don't know how feasible is that and what is the contact material). Since they sense the handpiece being put in the stand, they might be compensating somehow based on how long the handpiece has been held in hand, but this would only be a very minor adjustment. DC heater drive would be fine if synchronous rectification was used, such as the Linear replace-diode-bridge-with-mosfets chip. Otherwise rectifiers would dissipate a good few watts of power. Schottky rectifiers are no good, as they usually have relatively high reverse leakage current, which would distort thermocouple readings. The heater switch needs to be really high impedance in the off-stage. The AC switch which I have developed is cheap, simple and the power dissipation is negligible. The only important point is that the optocoupler collector-emitter voltage has to be higher that peak AC voltage. I really regret not being able to work on this project right now, as I could REALLY use a new iron. |
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