highaltitude.log.20080202

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[04:24] <Laurenceb> hey natrium42
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[09:13] <Hiena> Good morning!
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[12:55] <jcoxon> afternoon all
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[13:59] <jatkins> hi all
[14:00] <edmoore> hi jatkins
[14:01] <jatkins> I'm trying again to interface my camera to an Arduino
[14:01] <jatkins> with not much luck though
[14:02] <jatkins> I've got some resistors mc sent me, but I don't know to set them up as a voltage divider
[14:02] <jatkins> I'm trying to get 5V down to camera voltage (I think 3.3V)
[14:02] <edmoore> ok
[14:02] <edmoore> do you know about resistor colour codes?
[14:03] <jatkins> nope
[14:03] <jatkins> I know they're 1000 ohm each
[14:03] <edmoore> ok
[14:03] <jatkins> but I don't know how that translates to volts
[14:04] <jatkins> i.e. how many I need in the circuit to lower the voltage
[14:04] <edmoore> ok
[14:04] <edmoore> well the potential divider equation is really easy
[14:04] <jatkins> ok
[14:04] <edmoore> lets say you put 3 resistors end to end
[14:04] <jatkins> ok
[14:04] <edmoore> the bottom end connecting to ground, the top connecting to 5V
[14:05] <jatkins> ok
[14:05] <edmoore> they're all the same value (1000 ohm) so each resistor will have an equal 'voltage drop' across it
[14:05] <edmoore> the 3 resistors together drop 5V
[14:06] <edmoore> we know this, because one end is connected to 5V, the other to ground
[14:06] <jatkins> ok
[14:06] <edmoore> so by definition they have to be ropping 5V across them
[14:06] <edmoore> dropping*
[14:06] <jatkins> ok, thanks
[14:06] <edmoore> that means each other the 3 resistors drops 5/3V across it
[14:06] <edmoore> which is 1.6V
[14:07] <jatkins> they each drop 1V?
[14:07] <edmoore> 1.6V
[14:07] <edmoore> 5volts divided by 3 = 1.6
[14:07] <edmoore> well, 1.66666666....recurring
[14:07] <jatkins> ok
[14:07] <edmoore> so lets say we have a volt meter
[14:08] <edmoore> we put one end on ground
[14:08] <jatkins> ok
[14:09] <edmoore> we put the other end also on ground - the voltmeter will show 0V, because there is no voltage drop between ground and ground - obviously, as they're the same bit of wire
[14:09] <edmoore> then you take the 2nd end of the volt meter and put it above the first resistor that is attached to ground. it will show 1.6V
[14:09] <edmoore> because there is a 1.6V voltage drop between the ground and the resistor
[14:10] <jatkins> ok
[14:10] <edmoore> then you put it above the second resistor and ground, and it will show 3.3V, as there is a (1.6 x 2 = )3.3V (roughly!) voltage drop between 2 resistors and ground
[14:11] <jatkins> so the circuit should go something like this: shutter solder pad -> arduino GND, shutter solder pad -> resistor -> resistor -> arduino GPIO?
[14:11] <jatkins> using solder pads on either side of the shutter
[14:11] <edmoore> do you have a volt meter?
[14:12] <jatkins> yes
[14:12] <jatkins> well, a multimeter
[14:12] <jatkins> but that does the same thing?
[14:12] <edmoore> fantastic
[14:12] <edmoore> yes
[14:12] <edmoore> a multimeter can do voltage aswell as lots of other stuff
[14:12] <jatkins> yep
[14:12] <edmoore> could you stick it to the dial which says 20V
[14:12] <jatkins> ok
[14:12] <edmoore> and then put a probe on either side of the shutter solder pads
[14:13] <jatkins> ok
[14:13] <edmoore> with the camera turned on
[14:13] <jatkins> ok
[14:14] <jatkins> got it now, I'll have a go
[14:14] <edmoore> ok cool
[14:15] <jatkins> ah, probes not in the box
[14:15] <jatkins> it's very old
[14:16] <jatkins> could I just do it with wires soldered to the shutter pads?
[14:16] <edmoore> yep
[14:16] <edmoore> and connect them to the V and GND bits of the multimeter
[14:16] <jatkins> oh right cool
[14:17] <jatkins> it's got 3V and 5V bits, but not GND
[14:17] <jatkins> (that I can see)
[14:17] <jatkins> has a 'CONT'
[14:18] <edmoore> something black?
[14:19] <jatkins> there's a 'CCT Check'
[14:19] <jatkins> and 'Appliance Test'
[14:20] <jatkins> do you think I could use an analog GPIO without needing resistors?
[14:20] <jatkins> http://www.arduino.cc/en/Reference/AnalogWrite
[14:21] <jatkins> although either way I'll still need to probe the shutter
[14:22] <jatkins> but it could save using a resistor
[14:45] <edmoore> sorry jatkins, I got called away
[14:45] <edmoore> using a resisots is probably much easier than using a valuable hardware resource like an analogue pin
[14:47] <jatkins> ok, thanks
[14:48] <jatkins> because I may need to use an analogue pin for something else?
[15:01] <edmoore> maybe, yeah
[15:03] <jatkins> ok
[15:04] <jatkins> I'll have another look at the multimeter later, coming off now
[15:04] <jatkins> thanks though
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[18:56] <jatkins> hi all
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[20:58] <Laurenceb> http://pastebin.com/d1363b834
[20:59] <Laurenceb> a python gps parser I just wrote :P
[21:28] <Laurenceb> http://pastebin.com/d66caf5ef
[21:44] Action: Laurenceb ponders http://www.sstl.co.uk/documents/GNSS%20CASE%20Scholarship%20Advert%202008.pdf
[21:48] <Laurenceb> it looks very cool, but I'm not sure if I'm skilled enough
[21:51] <Laurenceb> edmoore_: what so you think?
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[00:00] --- Sun Feb 3 2008