High(ish)-speed Photography (followup)
Posted in Code, Guns, Photography, Technology on February 20th, 2009 by bemasher
So this Tuesday I got my Arduino in the mail. I really mean just in the mail… it was in an anti-static bag in a bubble-wrap envelope! Anyway I managed to waste about 6 hours screwing around with it the first night I got it. Since then after a lot of researching, googling, swearing and scratching my head I’ve successfully setup the first major part for the camera trigger project.
I discovered that the delay functions built into the Arduino C library are mostly useless. The microsecond delay function is most useless of all because it will only produce accurate delays between 4 microseconds and 16383 microseconds. So I gave up on that and just wrote a custom delay function. But before I wrote the custom delay function I looked at creating my own timer using Timer2 and giving up digital pins 11 and 3 for accurate times. Eventually I ditched this method because I never got any of the sample code to work at all.
Eventually I arrived at this at least reliable if not accurate delay function:
1 2 3 4 | void customDelay(unsigned long time) { unsigned long end_time = micros() + time; while(micros() < end_time); } |
The advantage to this over the delayMicroseconds() function is that this will at least pay attention to how long it’s actually been since it started where the delayMicroseconds() function just blindly sleeps for an arbitrary amount of time and wakes up when it sees fit. The function for oscillating the IR led at the frequency I needed for triggering the camera is of the same form just with a bit of code for switching the LED on and off twice every clock cycle in the while loop. It also turns out that changing the state of a digital pin isn’t near instantaneous either, which is to be expected. I’ve compensated for this using a constant defined for the number of microseconds it takes for it to turn a digital pin on or off.
Once I solved the timing issues it was essentially about cleaning up the code from that point on. I ended up storing the sequence of oscillation and pausing that Nikon SLR’s use in two arrays, one for oscillation and one for the matching pause between each oscillation period. Which makes for a clean section for firing the led and pausing all inside a for loop that iterates over each item in the two arrays.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 | /* Author: BeMasher Description: Code sample in C for firing the IR sequence that mimics the ML-L1 or ML-L3 IR remote control for most Nikon SLR's. Based off of: http://make.refractal.org/?p=3 http://www.cibomahto.com/2008/10/october-thing-a-day-day-7-nikon-camera-intervalometer-part-1/ http://ilpleut.be/doku.php/code:nikonremote:start http://www.bigmike.it/ircontrol/ Notes: This differs slightly from the other 3 versions I found in that this doesn't use the built in delay functions that the Arduino comes with. I discovered that they weren't accurate enough for the values I was trying to give them. The delayMicrosecond() function is only accurate between about 4uS and 16383uS which isn't a very workable range for the values we need to delay in for this project. The ASM code that Matt wrote works well but is limited to only pin 12 and I haven't got a good enough grasp of the architecture to modify the code to work on any pin. So this is what I've come up with to produce the same result. */ #define IR_LED 13 //Pin the IR LED is on #define DELAY 13 //Half of the clock cycle of a 38.4Khz signal #define DELAY_OFFSET 4 //The amount of time the micros() function takes to return a value #define SEQ_LEN 4 //The number of long's in the sequence unsigned long seq_on[] = {2000, 390, 410, 400}; //Period in uS the LED should oscillate unsigned long seq_off[] = {27830, 1580, 3580, 0}; //Period in uS that should be delayed between pulses void setup() { Serial.begin(19200); //Initialize Serial at 19200 baud pinMode(IR_LED, OUTPUT); //Set the IR_LED pin to output } void customDelay(unsigned long time) { unsigned long end_time = micros() + time; //Calculate when the function should return to it's caller while(micros() < end_time); //Do nothing 'till we get to the end time } void oscillationWrite(int pin, int time) { unsigned long end_time = micros() + time; //Calculate when function should return to it's caller while(micros() < end_time) { //Until we get to the end time oscillate the LED at 38.4Khz digitalWrite(pin, HIGH); customDelay(DELAY); digitalWrite(pin, LOW); customDelay(DELAY - DELAY_OFFSET); //Assume micros() takes about 4uS to return a value } } void triggerCamera() { for(int i = 0; i < SEQ_LEN; i++) { //For each long in the sequence oscillationWrite(IR_LED, seq_on[i]); //Oscillate for the current long's value in uS customDelay(seq_off[i]); //Delay for the current long's value in uS } customDelay(63200); //Wait about 63mS before repeating the sequence for(int i = 0; i < SEQ_LEN; i++) { oscillationWrite(IR_LED, seq_on[i]); customDelay(seq_off[i]); } } void loop() { if(Serial.available()) { //Wait 'till something is connected if(Serial.read() != 0) { //If anything but 0 is sent take a photo triggerCamera(); //Take a photo } delay(100); //Delay an arbitrary amount of time, serial isn't instantaneous } } |
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