Can I modulate FlexMod P3 (3.3) with 24V PWM signal

Can I modulate FlexMod P3 (3.3) with 24V PWM signal
I know It says 0-5v... but I have o way converting 0-25PWN signal into 0-5V without having reference 5v from somewhere and optocoupler.

Flex mod driven by 24V and I have only 24V PWN signal, driving 405nm laser.
I read somewhere that I can go upto 16V on M+ for modulation.

Can you guys suggest me some great idea when I don't have to add any active components to make it work?

BTW. I have no option but drive FlexMod with 24V, unless I come up with some extra switching DC-DC circuit to drop it to 9-12V etc....

Why would you need a voltage reference and an opto? Just use a resistive voltage divider to get down to 5V. Roughly 5:1 resistance would work (or do the math for exact values); Vin - 25k - Vout - 5k - Gnd/Rtn.

Sigurthr said:

Why would you need a voltage reference and an opto? Just use a resistive voltage divider to get down to 5V. Roughly 5:1 resistance would work (or do the math for exact values); Vin - 25k - Vout - 5k - Gnd/Rtn.

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Hey Tried that already, first thing actually (10k,2,7k)
But it does not work unfortunately....
Voltmeter shows 0-5V - looks great, when not attached to FLexMod
But when I attach this to M+ of FlexMod P3 that same spot M+ measures 9-ishV ( no matter what I supply by my voltage divider (0-5V) ) and therefore maxes output of the FlexMod!!!
so I believe voltage divider interference in some way with internal circuit of the FlexMod.
When M+ detached it measures 0.

Interesting. I can't find the schematic for the flexmod online. Here's the manual though: http://innolasers.com/laser/FlexModP3/FlexModP3_Manual.pdf . It claims the modulation input is protected and clamped. Can you measure the voltage between the M input and ground without anything connected to it? Might clue us in. Manual states an input impedance of 100k, so a 2k7 pull down in a Vdiv should actually sink the voltage, not raise it. Are you sure that the ground end of the 2k7 was actually connected, and that the grounds were continuous? If it wasn't continuous, then it could float the M to a higher voltage (probably the internal clamp voltage).

I was searching for schematic as well, could not find one , Thank you, I do have manual, I set it to 350mA for full, and 50mA for idle.

M+ and ground measures 4.9mV when not attached to anything.
2.7K definitely connected to the ground.


Can you explain "continuous ground" ?

Ya.... i guess Im SOL, check attachment, this is circuit which drives PWM E0-FAN in this case ( I'm reusing PWM controlled fan output to modulate laser )
No wonder its all messed up

Back to opto... and make 5V-16V using voltage divider from supplied 24V

E0-FAN+ is just the 24V rail, you won't see any modulation here. E0-FAN- is a switched ground connection; you can't use this for modulation as is either as it only switches a load connected in series with it. E0-FAN is probably an 8-12V signal, which would match the PWM output of whatever the controller is generating, and probably wouldn't mind sparing the handful of milliamps you need.

M+ reading as ~5V when nothing is attached shows that there is an internal pull up resistor of the flex mod, good info to have, but nothing unexpected or particularly helpful here.

You can't just input an oscillating square wave PWM signal into an analog modulation input and expect analog modulation either, that isn't how it works. You have to pass the square wave through a low pass filter (R in series, C in parallel) to form a demodulated signal for the analog input. The size of R and C are determined by the impedance of the load to be driven. You kinda need a scope for these kinds of things.

However, you can scale down that 8-12V signal to 5V and get TTL modulation, which will approximately match analog modulation in terms of brightness variation. You will have to measure the actual peak output voltage of the E0-FAN point, to do this place sufficiently large electrolytic capacitor (>10uF) across the multimeter leads (observe polarity, E0-FAN will be positive) and measure the voltage. Now remake the voltage divider as need to get 5V from the measured voltage. Apply the 5V TTL signal to the modulation input.

Sigurthr said:

E0-FAN is probably an 8-12V signal

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It is 0-5V goes to Atmega pin

Sigurthr said:

M+ reading as ~5V when nothing is attached shows that there is an internal pull up resistor of the flex mod, good info to have, but nothing unexpected or particularly helpful here.

Click to expand...

Actually It measures 5 milliVolts ... I think it marginally nothing.

Thank you for you great ideas! I will play with it, and will post result here with my results, also I have to treat that controller boards as black box and use only provided outputs.

Ah well if it's a 5V signal and logic level fet then that saves you from needing a voltage divider! Just place a series resistor of 10k-100k and feed that into M+.

Haha my bad about the ~5mV! Another reason I shouldn't reply via phone, easy to miss details on the small screen.

Sigurthr said:

Ah well if it's a 5V signal and logic level fet then that saves you from needing a voltage divider! Just place a series resistor of 10k-100k and feed that into M+.

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I cannot, I don't have access to that pin. unless I willing to mod the board!
So after poking around, I actually used opto, which let me to not care about whatever comes to E1-FAN+/E1-FAN- as long as it can trigger phototransistor.
I used salvaged from PSU PC817 added few current limiting resistors and 2 for voltage divider from 24V rail.... and voila!!! it worked
I will be making a post with photos etc about the whole assembly.

Did you set the P3's input and Offset potentiometers? If the input gain is turned to zero you will have no emission.

Steve

LSRFAQ said:

Did you set the P3's input and Offset potentiometers? If the input gain is turned to zero you will have no emission.

Steve

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Input and Offset? It has Gain (I assume Input), Balance and 0 Bias (I assume Offset) potentiometers... I did set those in a way that with 0 on M+ I have 10mA and with 5V I have 350mA.

even though you've done it , you could use a opto isolator with logic level output ,

The 24V PWM drives the led side , then 5V supplies the output side / modulation line .