So, something about this doesn't look right:
1,2 EN = Arduino's 5V
1A = PWM control signal
1Y = 3 TSAL6200 IR LEDs in parallel -> 100 Ohm resistor -> Arduino's ground
VCC1,VCC2 = Arduino's 5V
GROUND = Arduino's ground
For one, I am just now noticing that the TSAL6200 is rated to a max of 1.6V while I've been running at 5V (Nothing exploded). Given that the SN754410 is rated for a minimum 4.5V (maybe not the most appropriate part) I might have to step down the voltage on the output like this.
Second, it appears while the digital IO pin on the Arduino (what I am currently using) maxes at 40mA, the 3.3V line only does 50mA. There is no max listed for the 5V pin but one can assume comparable. This would imply I really can't drive the max amperage for the 3x LEDS (100mA each).
So, lets start again for an easy to acquire ~4.5 V supply, divide by 3 to be within the TSAL6200's max voltage, and add a draw of 300 mA:
Ohm's law:
0.3 A = 1.5V / x Ohm
5 Ohm = 1.5V / 0.3 A
Voltage Divider:
1.5V = ( Z2 / ( Z1 + Z2 ) ) * 4.5V
1/3V = ( Z2 / ( Z1 + Z2 ) )
I am guessing here but I think we want Z1 = 5 Ohm. With little confidence that is correct lets keep going:
Update: I've been corrected and we want Z2 to be 5 Ohm, see the comments for the new result.
1/3V = ( Z2 / ( 5 Ohms + Z2 ) )
5/3 Ohms + Z2/3 = Z2
5/3 Ohms = Z2 * 2 / 3
5 Ohms = Z2 * 2
2.5 Ohms = Z2
This gives:
1,2 EN = Arduino's 5V
1A = PWM control signal
1Y = 5 Ohm resistor -> 3 TSAL6200 IR LEDs in parallel -> Battery ground
-> 2.5 Ohms -> Battery ground
VCC1 = Arduino's 5V
VCC2 = 4.5V Battery
GROUND = Arduino's ground
So, where did I do it wrong?
4 comments:
Hi there,
I am an electrical engineer, so I might be able to help you out.
I have just found this post, because a friend of mine is a LT-enthousiastic. I haven't looked at your complete project yet, but it looks good.
Maybe you have some schematics, and using those I might be able to help you out, boosting the IR-leds output (should be easy).
Best regards,
Vince
Thanks. This was my best guess at the right way to do it. The maximum draw on the Arduino IO pins is 40 mA and it has left the base station a little finicky. You have to get the guns into the sweet spot in the IR led range to get anything close to reliable pickup.
I haven't gotten a chance to build the above yet. I got a comment that Z2 should actually be 5 Ohms to get the desired current across the LEDs. Then Z1 should be derived from there. This gives:
1/3 V = 5 Ohms / ( Z1 + 5 Ohms )
( Z1 + 5 Ohms ) = 15 Ohms
Z1 = 10 Ohms
I have yet to try it however. I need to pick up the additional small value resistors as my collection is fairly limited.
I didn't draw up actual schematics for this. The closest I have is the pictures I took of the current wiring with no additional amplification:
http://executedata.blogspot.com/2011/01/this-is-how-you-build-laser-tag-gun.html
I'll try to come up with something a little easier to read.
I am a little perplexed by the part creation in Eagle. Does anyone know a good library that contains the SN754410? The sparkfun libs have a part for the arduino sheild and at least some form of LEDs (wrong footprint but whatever).
Did you figure the correct circuit out? I am also looking to amplify TSAL6200 LED's for Lazer Tag projects on the Arduino.
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