Manual RGB 5v TTL Color Control Schematic/Diagram HELP

[markerney]

I am building a simple manual control board for my laser projector so that I can switch from my DAC (computer controller) to manual control and select color with one of SEVEN push button switches. I RECEIVED THE ATTACHED DIAGRAM from another photolexicon forum user. He suggests a very simple diode scheme that looks like it will work fine to me. I am no electronics expert but I have a basic knowledge and can put together a board from scratch if I know what to put on it. MY MAIN CONCERN is NOT TO DAMAGE MY LASERS! This is why I am posting this thread. Maybe we can all help each other and keep another laser ALIVE! Here is my delima .... The diagram attached shows diodes to keep voltage from feeding back but SHOULD I USE A LM7805 regulator at each output to insure the voltage does not go negative or below 4.8 or above 5.1 volts? How can I insure the output voltage never goes above or below 5v and NEVER GOES NEGATIVE? This is what I was told would insure I did not damage the TTL inputs on my lasers. If you say YES a LM7805 at each output is the solution then what values should the CAPACITORS be on the input and output of the LM7805 be? That is my TOTAL weakness. Calculating values. I am excellent with numbers but terrible with formulas! I will be using a 5v regulated input to the switches. Anybody who assists can have a NEGATIVE copy of the board when it is completed. I already have it layed out but I was wondering about adding PROTECTION for my laser TTL inputs before I etch it. Thank you sincerely for your time and consideration. Mark Erney

[mixedgas]

THIS ATTACHED CIRCUIT MEETS YOUR NEEDS FOR 5V, REVERSE PROTECTED.

YOU ONLY NEED ONE AT THE INPUT, NOT ONE FOR EACH LASER.
THIS WAY THE REGULATOR IS STABLE BECAUSE IT IS ALWAYS ON.

Steve

[markerney]

THIS ATTACHED CIRCUIT MEETS YOUR NEEDS FOR 5V, REVERSE PROTECTED.

YOU ONLY NEED ONE AT THE INPUT, NOT ONE FOR EACH LASER.
THIS WAY THE REGULATOR IS STABLE BECAUSE IT IS ALWAYS ON.

Steve

Ok ... That works but what if TWO buttons are pushed at the same time? What does +5 volts plus +5 volts equal? Would it not be better to use one at each output to insure my lasers get NOTHING except +5 volts at the TTL input? Saving components is not an issue at all. My main concern is protecting those TTL inputs on my lasers. BTW ... Thank you for the diagram! I am a dummy but the diagram makes it really easy to understand! WOULD I USE THE SAME VALUES IF I DID IT AT ALL THREE OUTPUTS? What is a lytac or lytic capacitor? Is that an abreviation for electrolytic? Really like the NOTE on keeping the output cap within 2.5 cm. I will send you a copy of the completed board. Please private me your email address and I will send it once it's done. I have another circuit I am working on that I have a few very SIMPLE questions on the values of the caps and resistors I should use. It is an 8 channel solenoid driver for effects that works off of a 5v TTL signal just like these color switches. Maybe you can help? I already have that board ready to etch. Maybe you can look it over and give me your opinion. I designed it using the manufacturer's recommended external components spec sheets. It uses (4) L295 drivers which will be heat sinked and handle up to 2 amps per channel. My solenoids draw only 500 milliamps each. It should be a fairly nice match.

[mixedgas]

The diodes prevent backtalk between any two lines. Just build it the way I have it and you will be fine. Lytic means electrolytic cap.

Older LM7805s oscillate with long cable loads, so the .1 uf is kept close to the 7805. They do not oscillate above 5V, so you would not see it without a oscilloscope. The 3 diodes around the 7805 protect you against reverse hookup.

You use ONE safe 7805 circuit to power the diode array drawing I posted earlier. The lasers draw about 1 milliamp,so you only need 1 7805 for the whole system.

Steve

[markerney]

Cool Steve! So no voltage change happens when two buttons are pushed at the same time? No matter how many buttons are pushed the voltage will always be 5 volts? I do have a dual trace oscope. Anything I should be looking for BEFORE I connect the outputs to my laser TTL inputs? I really appreciate your help! Your a COOL guy!

[mixedgas]

Cool Steve! So no voltage change happens when two buttons are pushed at the same time? No matter how many buttons are pushed the voltage will always be 5 volts? I do have a dual trace oscope. Anything I should be looking for BEFORE I connect the outputs to my laser TTL inputs? I really appreciate your help! Your a COOL guy!

end quote:

NO voltage change, the 7805 is a voltage regulator, it will hold 5V no matter what. Its good for up to a amp if its heatsinked. 5 volts divided by 470 ohms = 10.60 mA x 3 = 31.8 ma + the input current to the lasers, 50 ma tops. So your well below 1/20th of capacity with a lm7805 in a TO22o package.

yeah, just measure the 7805 being in the range of 4.90 to 5.15 volts and your fine. Put a small heatsink on the 7805 and keep in mind its tab is at ground potential.
As you hit each button you should see the Selected lines go from 0 to five volts minus a diode drop. A diode drop would be anywhere from .3 to .65 volts for silicon and no more then .32 for a schottkey. The TTL lasers should switch on at 2.4 to 3.2 volts and off at 1.6 volts or less, give or take. So even with the diode drop you have 4.4 volts, which is plenty.
Don't exceed 15V input to the 7805.

Steve

[markerney]

end quote:

NO voltage change, the 7805 is a voltage regulator, it will hold 5V no matter what. Its good for up to a amp if its heatsinked. 5 volts divided by 470 ohms = 10.60 mA x 3 = 31.8 ma + the input current to the lasers, 50 ma tops. So your well below 1/20th of capacity with a lm7805 in a TO22o package.

yeah, just measure the 7805 being in the range of 4.90 to 5.15 volts and your fine. Put a small heatsink on the 7805 and keep in mind its tab is at ground potential.
As you hit each button you should see the Selected lines go from 0 to five volts minus a diode drop. A diode drop would be anywhere from .3 to .65 volts for silicon and no more then .32 for a schottkey. The TTL lasers should switch on at 2.4 to 3.2 volts and off at 1.6 volts or less, give or take. So even with the diode drop you have 4.4 volts, which is plenty.
Don't exceed 15V input to the 7805.

Steve

Awesome Steve! Your information is excellent and easy to understand. You should write a book! "Laser Light Shows For Dummies". 2010 best seller! Here is the board I came up with thanks to you. I have a much bigger copy with 4 boards on it if you want a copy. Do you see anything that does not look right? I know you can figure where all of the components go of course. Did I goof anywhere? Thanks again friend! Mark

[mixedgas]

Looks good to me, as far as the board layout goes,.

Steve

[markerney]

Looks good to me, as far as the board layout goes,.

Steve

Good deal Steve! Is there anything you would add if you were making it?

[markerney]

Good deal Steve! Is there anything you would add if you were making it?

Was also wondering if you could help me a little with the values for this L295 circuit to drive my solenoids:

http://us1.st.com/stonline/products/...re/an/4032.pdf

It is a dual channel solenoid driver where the logic (TTL) can be a different voltage than the load. Each one has two channels and will handle 2 amps. I am using (4) on one board to give me a total of (8) TTL actuated channels. I just do not understand the formula for calculating the values for the resistors and capacitors. They provide values for the diodes. The circuit diagram and recommended board layout is FIGURE 14 on that PDF above. My solenoids are 24v and draw about 500 milliamps each. (4) will sometimes stay on and actuated for up to 5 or 10 minutes and the others will be on and off for beams. I am using a 15 amp regulated power supply for the power source for the solenoid load and the same 5v volt regulated supply I am using for the color board rated at 5 amps as the TTL source. Any help would be GREATLY GREATLY appreciated. Thanks again friend. Mark