Happy Father's Day to all the Dad's on the forum today.
First, let me just say how grateful I am for this site and the incredible help it is - I am a complete beginner and everyone has been very patient while offering much needed help.
In my continued mission for a play at home laser maze, I am now working on the laser control portion. Thank to elec mech, my display issues have been resolved.
After much thought about how to contol the lasers, I have been considering a shift in design. I really wanted a way to control the lasers individually and I think a controller like an arduino may in fact be a great option.
So, I have a few questions about this simplified laser circuit. If it passes your scrutiny, the end result would have up to 12 of the same set-up.
Number 1
Even though an arduino has 40mA per I/O pin, I had read that the I/O pins really shouldn't be used to drive external components. I had already ordered a 5V - 4A power supply back when the arduino was unknown to me, so I plan on just using that.
But, you will see I am using 2N3907 transistors which will be controlled by the arduino. I am trying desperately to learn from all of the help provided so I would like explain where I came up with my numbers and see if you agree.
The collector will have 5V from the Laser Power Supply. The laser runs/draws? approx. 25mA. The voltage drop across the 3907 is 0.7V. The base will have 5V from the arduino.
Based on previous help, I need 1/10th of the 25mA to the base.
So ... (5.0 - 0.7)/2.5mA = 2K base resisitor. Is that even close?
When Pin 22 goes HIGH, will the lasers light? Pin 22 LOW = Off? Will the transistor "protect" the arduino from any excess current issues, if that is a potential problem?
Number 2
I plan to use SCR's for the difficulty/start buttons. I have never used a SCR (yeah, I know you are surprised) and I am not sure if I can just use a resistor at the gate to trigger the SCR? If yes, is there something on the datasheet that would tell be what size?
If this new design direction works, I will be able to feed each LDR into an analog pin and "dial in" the sensitivity from 0 - 1023 units. My fingers are crossed that I haven't missed something.
Also, we sold our short bus that we used on vacations and I made sure I took out the PA/Siren/Animal Noise toy we had bought from Farm and Fleet. Thanks to elec mech, I now know how to measure the current that it draws: 31mA @ 12V. Needless to say I am still trying to figure out a way to get that to the party now too.
Anyway, I would appreciate feedback reagrding the "new" direction and specifically to my base resistor calculations and SCR question.
Thanks everyone,
First, let me just say how grateful I am for this site and the incredible help it is - I am a complete beginner and everyone has been very patient while offering much needed help.
In my continued mission for a play at home laser maze, I am now working on the laser control portion. Thank to elec mech, my display issues have been resolved.
After much thought about how to contol the lasers, I have been considering a shift in design. I really wanted a way to control the lasers individually and I think a controller like an arduino may in fact be a great option.
So, I have a few questions about this simplified laser circuit. If it passes your scrutiny, the end result would have up to 12 of the same set-up.
Number 1
Even though an arduino has 40mA per I/O pin, I had read that the I/O pins really shouldn't be used to drive external components. I had already ordered a 5V - 4A power supply back when the arduino was unknown to me, so I plan on just using that.
But, you will see I am using 2N3907 transistors which will be controlled by the arduino. I am trying desperately to learn from all of the help provided so I would like explain where I came up with my numbers and see if you agree.
The collector will have 5V from the Laser Power Supply. The laser runs/draws? approx. 25mA. The voltage drop across the 3907 is 0.7V. The base will have 5V from the arduino.
Based on previous help, I need 1/10th of the 25mA to the base.
So ... (5.0 - 0.7)/2.5mA = 2K base resisitor. Is that even close?
When Pin 22 goes HIGH, will the lasers light? Pin 22 LOW = Off? Will the transistor "protect" the arduino from any excess current issues, if that is a potential problem?
Number 2
I plan to use SCR's for the difficulty/start buttons. I have never used a SCR (yeah, I know you are surprised) and I am not sure if I can just use a resistor at the gate to trigger the SCR? If yes, is there something on the datasheet that would tell be what size?
If this new design direction works, I will be able to feed each LDR into an analog pin and "dial in" the sensitivity from 0 - 1023 units. My fingers are crossed that I haven't missed something.
Also, we sold our short bus that we used on vacations and I made sure I took out the PA/Siren/Animal Noise toy we had bought from Farm and Fleet. Thanks to elec mech, I now know how to measure the current that it draws: 31mA @ 12V. Needless to say I am still trying to figure out a way to get that to the party now too.
Anyway, I would appreciate feedback reagrding the "new" direction and specifically to my base resistor calculations and SCR question.
Thanks everyone,