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TTL modulation help needed

Posted by rastaman46 
TTL modulation help needed
August 30, 2016 01:26AM
Sorry for being noob to all this but I need some help

Got laser running on my printer finally !!!!

But got problem I think regarding TTL

TTL works fine on output from 0=V 255 = 5V

But laser turns on only on about 80% if less its just wont turn on (I can see that laser getting power coz there fan on top of the laser starts spin briefly )

What can cause this ? Not enough power? amperage?

On full power laser cuts paper fine but if I drop M106 S200 laser go off confused smiley


Thanks any one for your time

Regards
VDX
Re: TTL modulation help needed
August 30, 2016 02:37AM
... TTL is a binary mode - only suited for ON/OFF.

Some of the chinese vendors name analogue inputs with ranges from 0-5V TTL too, what's causing some fuzz eye rolling smiley

So it seems, you have a "binary" TTL input and have to control the power ratio by PWM (Pulse-Width-Modulation) - so the driver is set to the max. power and you'll reduce the average power by changing the PWM ration to a lower value -- e.g. 100% power with a 300µs PWM-periode is a power ratio of 295µs ON : 5µs OFF ... and 10% power ratio will be like 30µs ON : 270µs OFF.

I'm controlling the power with an external ArduinoProMini-clone in the laserdriver, which reads an analogue voltage (signal or potentiometer) for the pulse ON duration and gives this pulse length for every input pulse it receives, so I'm engraving with the 0.5µs Encoder-step pulses from the ArduinoDue and the effective pulse-length is defined per a potentiometer in my laserdriver ...


Viktor
Re: TTL modulation help needed
August 30, 2016 04:24AM
Thanks for reply Viktor

But I still really new to this

As far I understand that TTL Do laser ON/OFF right?

So PWM controls TTL from 0 - 255

So as far as I understand is that when TTL is on 127 I would expect laser to be at 50% power? im correct?

Thanks
VDX
Re: TTL modulation help needed
August 30, 2016 05:09AM
... no - with binary TTL you'll have a "threshold-level", which defines: below threshold = OFF /above threshold = ON ... your threshold level seems to be at around 80%

For changing the power you have to add PWM capability to your output.

There is soft-PWM for some pins, where a value below 255 will generate a pulse/pause-signal and reduce the output power by "averaging" the pulses over time ...


Viktor
Re: TTL modulation help needed
August 30, 2016 06:35AM
Thanks for reply again

So now I start to se light in end of the tunnel !!!

So on image2gcode I need to input "threshold-level" as minimum and 255 as maximum?

Thanks
Regards

Edited 1 time(s). Last edit at 08/30/2016 07:24AM by rastaman46.
VDX
Re: TTL modulation help needed
August 30, 2016 07:33AM
... your minimum is 0 (or <=204), your maximum is 255 (or >204).

For setting a power between complete OFF and constant ON you have to apply a pulse signal to your output pin, that switches between 0 and 255 - the switching frequency and pulse/pause holding times resp. the averaged times of 255 and 0 will then define your effective laser power ...


Viktor
Re: TTL modulation help needed
August 30, 2016 08:18AM
Thanks Viktor again

Ill give it a go tonight again and let you know outcome

Thanks
Regards
Re: TTL modulation help needed
August 30, 2016 12:41PM
Hi so i have changed min pover to 200 and max to 210 and its start burning but as not expected

it looks like laser never go off its just cuts square not image

see attached ?

Is that me missing something here or its jus G-code not right?


Regards

Edited 1 time(s). Last edit at 08/30/2016 12:41PM by rastaman46.
Attachments:
open | download - laser no go still.jpg (283 KB)
open | download - settings.jpg (109.1 KB)
Re: TTL modulation help needed
August 30, 2016 01:34PM
i believe the problem is with the gcode here.
try some simpler gcode to test. drawn as vector should be better, but if u would try with image based software, try it with binary image, only white and black pixels, no colors, no greys.
VDX
Re: TTL modulation help needed
August 30, 2016 01:43PM
... I can't correlate the burnt traces to the image - can you post a piece of your G-code, to see, what is sent to the firmware?

If your laser-driver has only binary TTL-input, it can't handle analogue voltages, but it should burn the black areas in the image, as they will give values above the threshold voltage.

Can you measure the output voltage and/or the pulses with a scope or DSO?


Viktor
Re: TTL modulation help needed
August 31, 2016 01:58AM
@okuzster thanks for reply ill try this

@VDX cant send gcode now but will sent it once I home

I don't have Scope or DSO.

It looks like gcode do its job but laser don't I have created short video to show whats going on

[youtu.be]

Thanks for your time again all

Regards
Re: TTL modulation help needed
August 31, 2016 06:22AM
On laser side I got this

Quote

Wavelength: 445nm (Blue)

Power: correspondence course 2500mW

Operating voltage: 12V (DC)

Working current: <1A

Idemitsu form: dot

Lens Material: dedicated optical coated glass

Cooling: Forced air

Shell material: aluminum anodized black

Input: 2.1 / 5.5 DC seat

And behind fan there is PCB to connect fan /main power and have writing TTL+ / TTL- confused smileyconfused smileyconfused smileyconfused smileyconfused smileyconfused smileyconfused smiley


Is here me trying to do something crazy or jus me gone crazy

Regards
Attachments:
open | download - 20160323030418_93756.jpg (169.9 KB)
VDX
Re: TTL modulation help needed
August 31, 2016 07:25AM
... could be, you're driving your laser not with TTL, but by switching the power ON/OFF, what's normally a really bad idea!

If the solder pads labelled [T+] [T-] are the TTL-input, then you should control it here with connecting GND to [T-] and your +5V-PWM-output to [T+].

But as this is one of this cheapish chinese driver boards, there could be a totally different circuitry behind, so you have to extract the complete electronic, to check it ... or get some more useful infos from the vendor ...


Viktor
Re: TTL modulation help needed
August 31, 2016 08:32AM
Thanks for reply Viktor

Can you explain me this Input: 2.1 / 5.5 DC seat

I struggling to find any info about it whats what

Regards
Re: TTL modulation help needed
August 31, 2016 08:47AM
So what would best approach to deal with it ?

Remove electronics an use 12V laser Driver ?

I got lost totally here

Regards
Re: TTL modulation help needed
August 31, 2016 10:54AM
It appears that you just have a laser head?

What brand laser?
ask seller to sell you a driver for laser.
angry smiley

Usually
12V high current main supply to laser --- conditioned down to 3.3v constant current diode supply
and
a trigger circuit to turn diode ON / OFF properly

forcing the diode supply ON / OFF NOT the way to do it.

confused smiley
VDX
Re: TTL modulation help needed
August 31, 2016 12:00PM
... the chines cloners often copy electronics without knowing exactly, what it's for ... and so the description can be miraculous too eye rolling smiley

It could be, this "2.1/5.5V DC" is the used TTL-level -- below 2.1V it would read LOW, above and to max. 5.5V it would read HIGH ... and above 5.5V it will burn.

But this is only guessed - get better infos or strip down the module and try to identify the correct inputs ...


Viktor
Re: TTL modulation help needed
August 31, 2016 12:53PM
Thanks for reply yes head only with built in constant current module

i have asked seller b4 purchase about ttl support and answer was yes

so i bet they tell u anything to sell it

Got totally lost here now
Re: TTL modulation help needed
August 31, 2016 12:56PM
Thanks for reply

That what im triyng to do now trying to take it apart to see whats inside

so all it is if i apply 12v to it it come on so that means T+ and T- do nothing i wouldn't expect laser to fire before T+ is 5V right?

Regards
VDX
Re: TTL modulation help needed
August 31, 2016 01:06PM
... try to identify the circuit - if there is some means of controlling, then you need the correct specs and input values.

If it's only a constant current (CC) module, the the T+/T- inputs will do nothing - but then, if it's a simple CC, you can switch the 12V with an external 12V driver, as if it were a TTL input.

But best would be to remove the actual driver and use a better one, suited and documented for "real life" use ...


Viktor
Re: TTL modulation help needed
August 31, 2016 01:52PM
Thanks for reply

So i got it all apart now see attached (I totally destroyed module but i dont care coz i managed to remove led safely )

and i have attached picture with all i got left can i make something with it or i need to buy some more stuff??

btw t+ go nowhere its just there

Regards
Attachments:
open | download - laser gunk 1.jpg (80.9 KB)
open | download - laser driver no good.jpg (89.7 KB)
open | download - all i got left.jpg (120.7 KB)
VDX
Re: TTL modulation help needed
August 31, 2016 04:11PM
... the previously "embedded" module seems to be a simple constant current driver, without any other controlling option.

The circuit in the red plastic housing seems to be one of the typical laserdiode drivers with TTL input, but with presoldered wires instead of plugs - here is one of this types:
Laser-driver

Was this driver with your lased-head?

Normally you have either a fix-current CC-driver in your diode head, or an adjustable driver like the last one - not both confused smiley


Viktor
VDX
Re: TTL modulation help needed
August 31, 2016 04:25PM
... on second thought -- could it be, that the "embedded" module is only the driver for the fan, and the laser-diode is only connected to the bigger external circuit?

Then this would be the typical assembly and the TTL-input is on the external module, not on the T+/T- pins inside the laser-head.

If so, then all laser power controlling was done with the external module and the laser head isn't running with 12V, but with around 4V and the current set with the blue potentiometer.


Viktor
Re: TTL modulation help needed
August 31, 2016 06:04PM
Not totally destroyed -- just needs to be soldered together

On your
20160323030418_93756.jpg

F-, F+ connected to fan
L-, L+ connected to laser diode
V-, V+ voltage supply

Where was the board in laser driver pix located?
What were grey and white wires connected to?

Where did circuit board on red plastic mount come from?

Stop jerkin us around and just tell us the driver on the red board
was in box you never unwrapped and used?


angry smiley
Re: TTL modulation help needed
August 31, 2016 07:26PM
Hey,

The last one is your laser driver. The one with a trimpot and a big inductor. Mine is the exact same. Mine does the exact same behavior when controlled via "standard" PWM from an Arduino.

The problem is simply that you are running the TTL input too fast. You can't switch at the "standard" speeds that your Arduino controller outputs. If it goes too fast for the TTL input on the driver can't keep up.

It is very possible that you can't get the switching speeds that you want in the end.

It is my impression that our Chinese friends have designed this "TTL" input to be for controlling the laser On/Off only- So not for use for dimming while burning. It is actually good that it has this feature because otherwise you have to cut power when turning On/Off and that has all sorts of bad effects on in-swings and so forth.

This is as far as I have gotten (determined why TTL will not work).

Personally my next step would have been to try and put an Arduino between the G-code interpreter (RAMPS) and the laser driver. Have that Arudino send the PWM at a much slower rate. See here how to adjust the PWM form:

[playground.arduino.cc]

BUT I have abandoned that project. As it happens, I have connected a device to measure current (A) from that Chinese driver and it is really bad. Fluctuating +-0.1A easily. While for pure burning that doesn't matter much , it does matter a lot if you want to control the exact dimness. So the fact that the driver can't keep stable current and it can't work fast TTL kinda tells me this is not the driver you want to use for exact dimming operations.

Edited 1 time(s). Last edit at 08/31/2016 07:37PM by LarsK.
Re: TTL modulation help needed
August 31, 2016 07:46PM
Hmm, my post sounded very negative.

Heads-up, the driver is fine for a lot of stuff. This week project:

LINK TO PHOTO

Double sided PCB for installation on my hot-end with power and Ethernet cable for signals. All made via VDX etching method and our Chinese laser driver using the TTL signal to control when it is burning or not. M42 P11 S255 and S0 respectively.
Re: TTL modulation help needed
September 01, 2016 12:25AM
Thanks for reply

Yes that little board with white stuff round it was inside

I have purchased this [www.aliexpress.com] separate to run on TTL that what seller refer me to.That why I got lost on this could not get it to work.

Can I use this driver to drive diode now? or I need something different?

Regards
Re: TTL modulation help needed
September 01, 2016 12:31AM
Thanks for reply

Driver in red box was purchased separate to run TTL

Seller refer me to this to run TTL (Looks like he have no idea what he selling)

Laser was 12DC with cc-driver built in (He description on laser isn't clear at all)

[www.aliexpress.com]


And he told me I need driver to run TTL refer me to this

[www.aliexpress.com]

Regards
VDX
Re: TTL modulation help needed
September 01, 2016 01:47AM
... OK, now it's a bit more clear ...

Your laser-head was previously only driven with a CC-driver (constant current) - but the 2500mW is not so clear either - there are actualy 445nm-laserdiodes with 1W, 1,6W, 2W, 3,5W and 6W available.

So the 2,5W is either an "overdriven" 2W-diode, or he gives not the optical output, but the drawn power -- so the laserdiode could be even a 1W-diode optically, that draws 2,5W power from the driver confused smiley

Your big driver is the corret one for TTL-driving.

Before connecting it to the diode, you should define the correct current level.

For this you must ensure, which laserdiode you have - either a 2W-diode with 1.7A max, or a 1W-diode with 1A max.

Then you connect the laserdiode-output to a 5Watt-resisitor with 0,1 Ohm and adjust the current through the resistor to the max. current you want drive your diode with.

You measure the current either with an Ampere-meter connected in series to the resistor, or by measuring the voltage across the resisitor and calculating the current with the formula:

I = U/R (I in Amperes, U in Volts, R in Ohms)

-- with a 0,1Ohm resisistor and measured voltage of let's say 150 Millivolts (=0,15V) this will give you a current of 1,5 Amperes ...

Edited 1 time(s). Last edit at 09/01/2016 01:48AM by VDX.

Viktor
Re: TTL modulation help needed
September 01, 2016 02:01AM
Thanks for reply

This is extremely helpful now much clearer.

But still got few questions

How do I identify diode ? how can I tell is it 1W or 2W?

Say if im not sure about Diode wattage yet if I set it to 1A to be safe ?

And voltage where do I start ? 3.3V? to max 5V?

Regards
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