confusion over TTl/PWM usage on web sites

  • Hi, I know the difference between PWM and TTL technically, but on the various web sites I have visited recently they seem to be used to mean different things! I the T2 software for example, are you referring to Non TTL lasers as the ones with only 2 wires IE no signal wire, or ones with the signal wire. Or are two wire lasers driven by the PWM output??
    So to be sure, On the Eleksmaker A3 pro with 3 wires (2500mw) would you refer to this as Non TTL, TTL, or PWM?

    Thanks very much

  • Developer of T2Laser Software

    @DavidF You are correct, there is plenty of confusion.

    I know you stated you know the difference technically but for others that don't.

    TTL is a definition of a voltage level. The voltage is either HIGH or LOW, this is used as a signal voltage to switch the laser on and off.

    PWM is a method of modulating the signal with varying pulse widths, the time or frequency remains the same (set in the firmware at compilation) but the on time vs off time during this time constant is varied. At 0% power the entire time period would be LOW or off, at 50% power the period would be equally split, with the signal at HIGH for half the time and LOW during the other half. At full power it would be HIGH for the entire time period.

    Here's an example from my oscilloscope showing 50% power (or duty cycle) with the default firmware using 1kHz frequency:

    So, your Eleks laser with 3-wires has TTL with PWM, that means it has a separate TTL input signal that is modulated using variable pulse widths (PWM) to switch the laser on and off quickly. This is the same way as all LED's work, since their diodes can't be on at half power like an incandescent filament bulb. Speed controllers for electric motors generally work the same as well.

    A non-TTL laser would typically have 2 wires, 12V and ground. This is the input voltage to the laser driver (a constant current source), this can be switching using PWM but the driver may not function correctly depending on it's design and the input frequency used.

    There are some lasers incorrectly sold as TTL which use a 12V PWM signal, TTL is never 12V so that's obviously wrong but they will work in a similar way except you can't drive them from the Nano's output directly (as that is a TTL PWM signal).

  • Thank you Zac for that clear explanation between TTL and PWM. Well done.

  • Perfect Zak, thanks.


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