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Thread: TTL and PWM

  1. #1
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    Default TTL and PWM

    Iím looking at some simple beam heads that have a TTL modulation input.
    Am I right in thinking that if I drive them with a PWM driver I can get some dimming or does that depend on type of TTL driver used?
    Iíve been looking at multi channel DMX led drivers, am I right in thinking that so long as they output the required switching voltage for the TTL driver it should work, or is there more to it than that?
    Feel like a total noob all over again!

    Any advice appreciated!
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  2. #2
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    Should work. Most cheapish LED drivers I have tested seem to all switch about 5K. You will need a "pull up" resistor as most drivers are open drain type. It will show as dashed lines if you are scanning.

  3. #3
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    Nope, not scanning. Just single beams. But possibly quite a few of them, and led drivers are a cheap way of getting lots channels

    Unfortunately got no real tech info about the head/driver so it will be testing required.
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  4. #4
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    Many lasers you say. Hmmm... So i've had this idea for a while maybe of use to your project? I think it would be possible to use ws2812 or better yet 2813 strings to modulate lasers. So, for example, If you had a bar of lasers you would use the 2812 chips as the mod source. A bunch of different "converters" are available to drive the ws2812 strings. Art-net, wifi artnet, dmx etc.

    edit: its 2811 that is needed. 2812 is the led and driver ic combined.
    Last edited by logsquared; 01-23-2019 at 16:02.

  5. #5
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    I was thinking more of just using something like this for the PWM. Plenty channels and cheap.
    Just need a housing, PSU, pre-punched panel for the outputs (more on that in a sec...) and some form of estop, probably just another relay to cut 12V power.
    |
    https://www.amazon.co.uk/LEDEMAI-Cha.../dp/B01E6M6RFE
    |
    The units themselves take power and trigger on a 3 pin connector (XLR - Gnd, 12V, TTL)
    I am REALLY nervous of having 3 pin XLR floating around the place with 12V on it - I can see DMX fixtures going up in smoke from well meaning hands plugging stuff in all over the place.
    |
    As we'd be having them made up to order, there is the possibility of specifying another connector. They have suggested RJ45 but I'm not totally convinced.
    |
    The XLR is compelling, because 3 pin DMX cable is readily available and we already have lots of it. Anything else would require custom cables made up.
    |
    What other options might there be for 3 pin (min) locking connector that fits a D panel hole and isn't (commonly) used in a lighting environment already?
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  6. #6
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    Its if something can get plugged in wrong it will eventually happen. RJ45 would be probably be less likely to get swapped but ethercon is pretty expensive. I don't think 12v will damage a fixture as rs485 receiver should take 12V. Not sure about the transmitter end. I would think 12v shouldn't kill it. I would research it to be sure.

    I would be worried about sending TTL along with power over any real distance. Due to voltage drop you could end up with ground at the end being several volts above the TTL ground. Depends on the wire length, gauge and current draw.

  7. #7
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    ... I'm TTL-/Pulse-driving my lasers or high power UV-LED's with different types of (selfmade) drivers - the simplest types are around one (or more in parallel for higher current) LM317 as constant current drivers (needs only a shunt resistor to set the current) -- and then simply switching the voltage to the LM317 with a MOSFET, that is driven with TTL signals (5V-pulses) from an Arduino.

    With an Arduino Nano it's like 6 Microsenconds shortest +5V-pulse-duration to contiuous +5V-output - with 5V at the MOSFET gate, the driver gives the set current to the LED (or laser) ... and with pulsing and pulse/pause-ratio I can define/change the "visible" (or "averaged") power from 0% to 100% without problems

    Viktor
    Aufruf zum Projekt "MŁll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  8. #8
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    Chris, I don't think any run would be excessively long (~50m)
    With LED drivers so cheap, we'd probably build a couple of control units, so we could place a driver near a group of heads with single DMX line to it, rather than one big driver feeding lots of heads a long way away. The cost of the controller would be less than the cost of the extra cabling.

    Interesting to know about the DMX, I'll have to look into it. DMX cable would be so very, very straightforward and cost effective.
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  9. #9
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    Interested to see how you're project turns out. Sounds cool. Will the heads be RGB?

    I found these DMX RGB controllers on ebay :https://www.ebay.com/itm/MINI-3CH-dm...Ud2:rk:27:pf:0 I have not used this particular unit but have used similar without DIP addressing and they are reliable. If you went DMX to each head then you would have to send power to each head too. I see the benefit of sending one cable (power plus signal) to each head.

    I did a quick calculation for a 50m 20awg mic cord with 1 amp. The voltage at the end would be ~9V. Honestly, 50M seems pretty far to send TTL too. I have sent SPI (pixel protocol) which is also unbalanced over mic cords. I have found 10M is the longest I can go before the signal is too degraded.

    I am probably making this to complicated. I have a tendency to do that. HAHA. I wonder how hard it would be to make power over DMX "POD" ? Basically the DMX +/- line would carry the +12V and the shield would be ground. If the receiver chip had a common mode rejection of 12V it should work without modification. Injecting the power on the transmitter side might be a bit harder. You would have to use a DMX splitter and still send an individual line to each head instead of the typical daisy chain to keep the current low. Depending on current a few heads could possible be chained together.

  10. #10
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    ... my pulsed drivers all runs with optocouplers - this could be long (up to Kilometers) optical fibers too

    So a power-source nearby the driver ... and signal feeding from any distance per opt. fiber

    Viktor
    Aufruf zum Projekt "MŁll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

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