Amplifying a TTL signal?

[things]

Hi, I recently bought a nice >100mw green laser module, and I need to put it into my laser scanner. I tried it this afternoon, but the TTL output from the control board isnt strong enough to fully trigger the laser, resulting in a very dull and distorted dot. Does anyone know how I could amplify this 5V signal? I only need to increase the current, the voltage must stay at 5V. I would prefer if it ran from 5V input, but it can use 15V if necessary.

Thanks

 

[3v0]

It would be better if one of the hardware guys answered this. If I get it
wrong they will let us know.

I do not know much about lasers. Are you trying to switch the power feed
to the laser?

If so you need to know what current the laser draws. The 100mw is the output
power.

If the input current is 600 mA or less I would try using a 2n2222 to switch the laser ground. Use a 1K resistor between the TTL and the transistor base. Hook the collector to the laser ground and ground the emitter.

The problem is that there is going to be a voltage drop across the transistor. If it reduces the voltage too much, use an adjustable voltage regulator on the 15V supply and regulate to 5V+(the drop) so that the laser see 5V. Feed the + on the laser with this.

Are you doing this https://www.instructables.com/id/3-D-Laser-Scanner/

Hi, I recently bought a nice >100mw green laser module, and I need to put it into my laser scanner. I tried it this afternoon, but the TTL output from the control board isnt strong enough to fully trigger the laser, resulting in a very dull and distorted dot. Does anyone know how I could amplify this 5V signal? I only need to increase the current, the voltage must stay at 5V. I would prefer if it ran from 5V input, but it can use 15V if necessary.

Thanks

 

[things]

Hi 3v0, The laser driver board already has a trigger circuit built in. Basically, it has a little socket where you can supply it 5V for blanking. So, I do not need to switch the power for the laser, the driver board does that, but basically I need to amplify the OUTPUT TTL signal from the control board.

TTL is just a On or off signal. 5V means on, 0V means off. So basically the board supplying the TTL signal isnt supplying enough power into the laser driver board, to cause it to turn on the laser to full power. I just need to add abit more push behind the already existing 5V signal.

Hope that clears it up abit

 

[Boncuk]

What else do you want?

3V0 already stated clearly that a low power transistor would do it!

If the TTL-output is too weak this is an effective and cheap way to increase power on the laser.

Boncuk

 

[things]

I was just saying, he was thinking I was powering the laser DIRECTLY from the 5V, but im not, so I was just clearing that up.

 

[rezer]

I am trying to understand your problem. You have a 5V TTL signal that is being output from the control board to the laser to trigger it? Is this correct? By amplify you mean the current?
If this is correct, I am assuming your 5V signal is being loaded by your scanner laser. Have you measured the signal for full swing (0-5V)? If it is running at 0-5V swing, than using a "bigger" transistor to sink more current won't do you any good since your trigger circuit is already providing ample power for triggering. If you need more current, than 3v0s solution will work if your system doesn't mind the inversion. Else you can use an NPN/PNP or NPN/NPN combination for non-inverting.
Sorry if my analysis is wrong here but I am just wondering if you have considered everything.

 

[kchriste]

TTL is just a On or off signal. 5V means on, 0V means off. So basically the board supplying the TTL signal isnt supplying enough power into the laser driver board, to cause it to turn on the laser to full power. I just need to add abit more push behind the already existing 5V signal.

Are you driving the trigger circuit from an actual 74LSxx chip? It could be that all you need is a 4.7KΩ pullup resistor so that the TTL signal goes closer to 5V when high. Do you have a scope to measure the signal you are feeding it?

 

[things]

Hi. Upon DMM'ing the signal, it appears to be only going to 1.5V!!! So, really I just need a transistor that can trigger at 1.5V, and is fast. The laser PSU has 5V output, so I can use that to power the TTL signal aswell.

 

[things]

I have a TIP41C transistor here if that will work? Will it work with about 0-3V in, and be able to pass 5V?

 

[Torben]

I have a TIP41C transistor here if that will work? Will it work with about 0-3V in, and be able to pass 5V?

Hi Things,

According to the TIP41C datasheet it should be more than able to handle the job. It's hard to say how fast will be fast enough for your needs, so maybe it's not fast enough. I don't know.

I'd suggest going more for something like 3v0's suggestion of the 2N2222 (or even a 2N3904). I would think either would be able to do the job as I don't expect you will need much current capability just to flip the trigger. Relative to the low current I think you need, the TIP41C is a monster at 6A current capability. It would work but it would be like driving a tank to the corner store for milk.


Torben

 

[ericgibbs]

Hi. Upon DMM'ing the signal, it appears to be only going to 1.5V!!! So, really I just need a transistor that can trigger at 1.5V, and is fast. The laser PSU has 5V output, so I can use that to power the TTL signal aswell.

hi things,
Are you measuring a TTL 'pulse' with a DMM.?
If yes, if the pulse is of a short duration, the DMM will not give a true reading.

You need a scope.

IIUC are you trying to amplify the TTL trigger pulse to the laser.?
Whats the laser spec for the pulse.?

 

[Torben]

hi things,
Are you measuring a TTL 'pulse' with a DMM.?
If yes, if the pulse is of a short duration, the DMM will not give a true reading.

You need a scope.

IIUC are you trying to amplify the TTL trigger pulse to the laser.?
Whats the laser spec for the pulse.?

Morning Eric!

I was hoping that the thing works with a high meaning "laser on" and low meaning "laser off", but you're right: it could just be a pulse.

Hm. Now that I think about it, and my idea above was correct (which I think the OP's second post indicates), then shouldn't any voltage over the TTL trigger level force the laser full on, with some hysteresis before a voltage drop on the trigger line would turn the laser back off again? If I'm right about that, I wonder why a middling trigger voltage would turn the laser on at all--I'd have thought it would either be full on or full off, if there was enough voltage on the trigger line to turn it on at all.

I imagine I'm just missing something here. I'm pretty tired. It's been a full week.


Torben

 

[things]

I quickly tried the circuit I posted below, and the laser just stays on continously. no blanking at all. When there is NO signal to the laser driver, the laser is supposed to be off. So if its straight on then that means the transistor is connecting it to the 5V supply.

Here is what i did.

**broken link removed**

 

[things]

On the pic, the bottom connection to the laser goes to -, and top goes to +

wait, does the transistor need some sort of + supply to work??

 

[Torben]

I quickly tried the circuit I posted below, and the laser just stays on continously. no blanking at all. When there is NO signal to the laser driver, the laser is supposed to be off. So if its straight on then that means the transistor is connecting it to the 5V supply.

Here is what i did.

**broken link removed**

Try putting a 1k resistor in series with the base like 3v0 said and put a 1k resistor between the collector and +V. Then connect the collector to the laser's trigger input:

Again, I'd suggest going for a smaller transistor than the TIP41C if you have any around.


Torben

 

[things]

Bah it still isnt working. I dont get it

 

[Torben]

Bah it still isnt working. I dont get it

In what way did it not work? Laser on all the time, off all the time, weak, blew up, turned into a duck. . .?

Can you post a link to a datasheet for the laser? Post a schematic of what you have set up and a (clear) photo of the circuit so we can see the connections, if you can.


Torben

 

[ericgibbs]

In what way did it not work? Laser on all the time, off all the time, weak, blew up, turned into a duck. . .?

Can you post a link to a datasheet for the laser? Post a schematic of what you have set up and a (clear) photo of the circuit so we can see the connections, if you can.


Torben

Morning Torben,
Your circuit should give a good pulse to the trigger.

Things, you must give us more input if we are to help you.

 

[things]

I just discovered something. I compeletely removed all the wires except for the TTL in and the 5V in. It turns out that the laser pulse is controlled by the +! I could completely remove the ground signal wire and it still worked, when I removed the + wire it went out. SO somehow I need the transistor to switch + voltage. Any ideas?

 

[Torben]

I just discovered something. I compeletely removed all the wires except for the TTL in and the 5V in. It turns out that the laser pulse is controlled by the +! I could completely remove the ground signal wire and it still worked, when I removed the + wire it went out. SO somehow I need the transistor to switch + voltage. Any ideas?

Can you post a schematic or diagram of what you have?


Torben

[Edit: In particular, I'm interested in the output from the control board. What is sending the pulse? A transistor? A buffer? A TTL 74xx chip? That would help us know what it is capable of.]