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February 16, 2011
about 3 years ago
With only minor changes the current board can be adapted to accurately measure 1000 cps.
Without changing the code at all, changing C2 to 670 nF, R10 to 20K, adding a 4k resistor to the collector of Q4 (desoldering and connecting the resistor), and changing C9 to 300 nF will give a 1000 cps functionality (confirmed) with about a 1% overcount due to events that happen right before a power supply switch.
The power supply design does produce a lot of noise at the “sig” signal if the R10 and C9 values aren’t huge.
This can be nearly fully corrected in software by merely ensuring the interrupt remains low for more than XX microseconds (a 100 uS pulse is generally much larger than the supply noise pulses with the smaller RC time constant and can be used to determine that the interrupt was due to an actual cascade event and not just the power supply noise).
I kinda liked this kit. It works and it’s a nice tool for understanding simple boost conversion, capacitive coupling, and RC filtering. Although, would it have killed you guys to add an oscillator footprint on the board (even if you didn’t include the oscillator?) ;) I soldered an 8 MHz oscillator to the 328P by hand and just reprogram the device through the Arduino IDE as a mini/micro 8mhz 5v it seems that the $1 expense to make this Arduino compatible (without messing with fuse settings) would be worth it. Also, serial communication on an internal RC oscillator is sketchy (I realize the current design just works by sending asynchronous noise over a serial connection, but modifying the device to send cpm/cps/cph is tough without an oscillator).
What software are you using to program the board? I’m assuming AVRdude is being used by something else (like AVR studio or the Arduino programming environment).
One thing to note with his board is you NEED to make sure when you program the thing that your fuse settings specify the internal RC oscillator in the 328P. If you try to program this chip and you set the fuses to use an external resonator, you’re in trouble.
My guess is that you accidentally programmed the thing with fuse settings that specified an external oscillator (no oscillator is connected). If this is what you did (and I suspect it’s what you did, you might just want to get yourself a fine-tipped soldering iron and solder an oscillator to the chip so it has an external crystal oscillator. I really don’t know why Sparkfun didn’t splurge for the $1 oscillator on a $150 board. If they had, this thing could be programmed REALLY easily. It could even ship with the arduino bootloader so people could just program the thing from the serial port and not worry about the ISP programmer.
News - July Caption Contest Time…
about 3 years ago
… tryin' to catch me ridin' purdy.
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