Author Topic: Pull down resistor on mana SE board  (Read 181 times)

Romoshka

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Pull down resistor on mana SE board
« on: May 30, 2018, 10:49:33 AM »
I am not one to ask what probably is a silly/easy question without doing the searching. In part because it's rude and lazy but I also like to hide my ignorance when possible.  I can not find where to install the pull down resistor, to disable the momentary laser on condition, on my mana SE board.  I see photos showing it bridging across a TTL pin set but alas no such label exists on my board.  To reveal the full magnitude of  my ignorance I don't know what a TTL even is and after reading several paragraphs on TTL I'm no smarter.
Much work remains to be done before we can announce our total failure to make any progress.

ggallant571

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Re: Pull down resistor on mana SE board
« Reply #1 on: May 30, 2018, 11:41:06 AM »
Do you have a 3-wire interface from the controller to the laser module?
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Romoshka

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Re: Pull down resistor on mana SE board
« Reply #2 on: May 30, 2018, 01:35:04 PM »
Yes, there is a 3 wire connector between laser and board.
Much work remains to be done before we can announce our total failure to make any progress.

Zax

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Re: Pull down resistor on mana SE board
« Reply #3 on: May 30, 2018, 02:10:36 PM »
One of those should be labelled S (signal), connect the resistor from that wire to - (ground).

ggallant571

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Re: Pull down resistor on mana SE board
« Reply #4 on: May 30, 2018, 02:44:16 PM »
Typically wire color code:

RED is +12V, BLACK is GND, other is PWM signal.
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Zax

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Re: Pull down resistor on mana SE board
« Reply #5 on: May 30, 2018, 03:16:23 PM »
You would think so, but Chinese logic doesn't always follow conventional wisdom. I think they prefer random wire color selection.

Romoshka

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Re: Pull down resistor on mana SE board
« Reply #6 on: May 30, 2018, 03:53:45 PM »
Yes,
+ red
- Blk
S yellow
Awesome. Thank you.   I see many references to best resistor size.  Is there a consensus yet?
Much work remains to be done before we can announce our total failure to make any progress.

ggallant571

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Re: Pull down resistor on mana SE board
« Reply #7 on: May 30, 2018, 04:08:29 PM »
The worlds foremost expert on pull down resistors (me) says 4.7K (or 3.3K or 2.2K).
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Romoshka

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Re: Pull down resistor on mana SE board
« Reply #8 on: May 30, 2018, 05:28:26 PM »
Glad to hear the jury is in.  Thanks so much.
Much work remains to be done before we can announce our total failure to make any progress.

Romoshka

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Re: Pull down resistor on mana SE board
« Reply #9 on: May 30, 2018, 05:40:57 PM »
Oh, and to both further my education and show more of my ignorance, you say the 3rd wire is PWM signal.  I'll assume that the S on the board is for signal but what is PWM?
Much work remains to be done before we can announce our total failure to make any progress.

ggallant571

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Re: Pull down resistor on mana SE board
« Reply #10 on: May 30, 2018, 07:07:19 PM »
The S probably stands for "Signal". By switching the laser ON/OFF at a fairly high rate it simulates a variable power level. PWM stands for Pulse Width Modulation. With our GRBL firmware a value of 0 means all OFF, 255 means all ON, 128 would be about 50% ON//OFF.
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Romoshka

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Re: Pull down resistor on mana SE board
« Reply #11 on: May 30, 2018, 07:33:45 PM »
Thank you sir.
Much work remains to be done before we can announce our total failure to make any progress.

Zax

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Re: Pull down resistor on mana SE board
« Reply #12 on: May 31, 2018, 04:31:18 AM »
The other term you'll see a lot, is TTL. Your "signal" is TTL (transistor-transistor logic) which just means it's based on 5V logic and as ggallant571 said it's switched on/off at around 1kHz (typically) which is a method called PWM. The frequency remains the same but the on to off time is varied, thus creating the pulse width modulation or mark-space ratio in electronic terms.

Oh, and the worlds second most expert (me) has found a 1kohm resistor was needed on one of his boards  ;)

Romoshka

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Re: Pull down resistor on mana SE board
« Reply #13 on: June 12, 2018, 07:17:36 PM »
Thanks to all for all the help.  Pull down resistor soldering place with the help of some loupes...boY is that a small space. 
Much work remains to be done before we can announce our total failure to make any progress.