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16  Forum 2005-2010 (read only) / Interfacing / Matrix lib/MAX7219 wrong ouput? on: July 17, 2008, 12:39:51 am
Hi,

I've just received my samples from Maxim and have been playing around. At first I thought a bunch of the chips were damaged as I have only connected 8 LEDS and none of them were turning on. I checked through several tutorials for the matrix library and checked all my connections. however nothing turned on. Then I though well lets play around a little and turn one out of 8 leds on from each of the 8 outputs. Low and behold an LED turns on. However it was the wrong one. On futher examination -everything is backwards. The array is [0-7][0-7] if you use row 0 then row 7 actually turns on, same with the individual  LED's the 0 output turns on led 7. And yes I've checked everything over and over, so either the library is backwards, or the datasheet is backwards, take your pick. Just thought I'd ask if anyone else has come across this little slip up and if there is a decent work around besides wiring everything in reverse.

Justin
17  Forum 2005-2010 (read only) / Interfacing / Re: tach input on: July 21, 2008, 04:46:52 am
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I would have thought it better to use the tach signal as an interrupt.. and every time the interrupt is serviced, check 'millis' and see the time difference.. Divide that result by the number of milliseconds in 1 minute.  Average the value over about 10 pulses or so to get a somewhat stable signal and you should have what you are looking for.

Then you need to divide that number by the number of pulses per revolution... IE: for most 4cyl it is 2 pulse per rev.

You will want very efficient code... if you load down too much process time your RPM result will be inaccurate.

Exactly the reason I'd rather use freq to voltage conversion. If your using the arduino to do anything reasonably usefull with the tach signal, then you will want all the cycles you can get, better to use something accurate (the F2V converter) and just read its value when you need it.
18  Forum 2005-2010 (read only) / Interfacing / Re: tach input on: July 19, 2008, 09:40:58 am
frequency to voltage converter is probably the best option....well its the option I will be taking for both VSS and Tach readings, and I can't think of a better way to do it without taking up a lot of cpu cycles just trying to measure pulse frequency.
19  Forum 2005-2010 (read only) / Interfacing / PWM control of solenoid/motor with feedback on: July 06, 2008, 04:30:39 am
I recently had to design a drive circuit which takes 5V logic on/off/pwm and drives a low impedance load driven from a higher and varying voltage source. Its use in this case is driving the transmission solenoids in an automatic gearbox where current controls the line pressure and hence the shift firmness. Since the voltage level in a car varies quite widely depending on battery charge, temperature etc, and the current has to be consistent even if the solenoid resistance changes so a feedback system has been used. Also as the gearbox solenoids have a tendency to sometimes go closed circuit when they fail a current limiting driver has been used.

I thought this design might help a few out there who are planning on driving motors or low impedance solenoids with a max current around the 1.5-2A mark.

http://delta.uni.cc/car/solenoiddriver.asc
Circuit was designed in SwitcherCAD/LTSpice.
20  Forum 2005-2010 (read only) / News / Re: DuinoStamp - Tiny board with just enough. on: July 06, 2008, 02:37:04 am
Hi everyone I'm new to the forum. But reasonably aged in the microprocessor area. My real name is Justin and I was involved in the design of these. Currently waiting for my shipment of them to arrive smiley Can't wait to get them and give them a workout. I'd like to say a big public thank you to spiffed for taking my idea and making it a reality. I'm still spun out about the low price.

Justin
21  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Java programming on: July 06, 2008, 02:33:05 am
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Im interested in the arduino. but my programming backgroud is in java. Can the arduino be programmed using java?

If you are fluent in Java, then programming in C/C++ is not going to be that hard for you. The syntax is very similar and all you really need to learn are the calls for the specific libraries you will be using. Don't be phased by the fact that you have never programmed in C/C++.
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