#3360688 - 08/06/11 10:04 PM
DIY Air-Core Gauge Electronics
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Joined: May 2006
Posts: 114
Mike Powell
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Member
Joined: May 2006
Posts: 114
California, US
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I'm trying my hand at using SMD parts for the circuitry which will drive a hand made air-core movement. The electronics is based on a PIC16F648A micro controller. It connects to an L293DD which will drive the air-core (or a Switech stepper gauge movement). The PIC takes data from a multi drop bus. That's what the pair of DB-15 connectors is for. I'm using "giant" SMD parts. The resistors are .12" by .06" and the ICs have a .050" pin spacing. The finished board size is 2.4" by 2.4".
Last edited by Mike Powell; 08/06/11 10:05 PM.
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#3368549 - 08/16/11 09:03 PM
Re: DIY Air-Core Gauge Electronics
[Re: Mike Powell]
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Joined: May 2006
Posts: 114
Mike Powell
Member
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Member
Joined: May 2006
Posts: 114
California, US
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Well, the circuit boards were delivered yesterday, and I've (mostly) assembled one. This is my first project using surface mount components. Other than some issues resulting from my not properly cleaning the board before soldering, assembly proceeded okay. I used a 2X magnifying glass and a soldering pencil with a 0.8mm tip. It's configured for in-circuit programming using a PICkit2. The PICkit recognizes the microcontroller and can read its memory. At this point I don't have the firmware converted to program it. Actually, I don't even have the Microchip programming tools loaded on my system. Guess I better do that soon. Anyway... Depending on what firmware the PIC runs, the board can drive an air-core movement, or a Switech stepping motor gauge movement, or a small generic stepping motor, or up to four RC servos.
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#3368894 - 08/17/11 12:57 PM
Re: DIY Air-Core Gauge Electronics
[Re: Mike Powell]
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Joined: Jan 2004
Posts: 1,221
f15sim
More projects than sense!
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More projects than sense!
Member
Joined: Jan 2004
Posts: 1,221
Graham, WA
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*cough*ATMega328*cough* Great job Mike. g.
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#3369566 - 08/18/11 10:35 AM
Re: DIY Air-Core Gauge Electronics
[Re: Mike Powell]
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Joined: Nov 2005
Posts: 557
GrizzlyT
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Member
Joined: Nov 2005
Posts: 557
Sterling Heights, Michigan
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With all the talk of making it smaller and Mike's (meant to be humorous) reference to these SMDs as "giant", I just had to chime in.... Especially since SMT is what I do to pay for the sim. my day job I had to snicker at the "giant" reference because, in the industry, that's not far from the truth. 1206 and 1210 packages (.120" x .060" & .120" x .100") were the standard about 10-12 years ago. Nearly every passive component we place these days is 0402 to 0603 case sizes. And we do place 0201 components. Actually the latest case size is 01005, which is only .010" x .005". (Think finely ground pepper.) I was looking at the PCB thinking, "yeah, the 8SO could probably be shrunk to a SOT, the 20SOLs could go to SSOPs, the passives to 0805, etc.." And while our machines help to make the job faster...re-work is still done by hand, under a microscope. So when you talk about soldering difficulty?.....I feel your pain.
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#3370325 - 08/19/11 08:11 AM
Re: DIY Air-Core Gauge Electronics
[Re: Mike Powell]
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Joined: Nov 2005
Posts: 557
GrizzlyT
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Member
Joined: Nov 2005
Posts: 557
Sterling Heights, Michigan
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For me, I think using SMDs is probably easier overall. Maybe it's because the soldering isn't a big issue? (That's what lunch breaks at work are for. ) When I etch my own PCBs, I try to keep it 1-sided and not have to worry about screwing up the alignment. (I just add a couple jumper wires, where I can't get around crossing 'em.) So, when I can use SMDs, it eliminates most of the drilling. And I really hate all the micro drilling! And when you have to go 2-sided, there are no sleeves in the vias, either. So, you end up doing twice the soldering, with thru-hole, to tie the top and bottom annular rings. Maybe I should get out of the PCB making game and just let a board house do it?! I'm curious, who did you use to fab it? And did you get stuck with a big setup fee, for the small run? And if it's not too personal....how much?
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#3374929 - 08/25/11 10:49 PM
Re: DIY Air-Core Gauge Electronics
[Re: Mike Powell]
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Joined: May 2006
Posts: 114
Mike Powell
Member
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Member
Joined: May 2006
Posts: 114
California, US
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I got the firmware together and loaded into the PIC. I added a bit of self-test code since I'm currently too lazy to re-create the PC-based test code I lost awhile back. The self-test code simply increments the data for the air-core movement shaft position each time a PWM cycle completes then sets a flag indicating new data. The PIC executes its code as though it had received a command from the host computer. As I write this, the PIC is causing the air-core movement to rotate its shaft about once a second, so mostly I'm happy. The part I've not tested is the comm functionality. I've used the firmware in other projects, so I don't expect any big issues there, however... Something I just read in the PIC docs make me think that using the receive functionality of the USART may preclude using the TX pin for a general output pin. Guess I'll just have to crank up MSVC++ and re-create the PC-based test code.
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