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Press on press off

Discussion in 'General Electronics Discussion' started by outinthewoodsnf, Nov 30, 2020.

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  1. outinthewoodsnf

    outinthewoodsnf

    6
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    Nov 30, 2020
    Hi,
    I'm no expert in electronics, I'm hoping that someone can help me..I have a Dewalt line laser that I want to come on when power is put on the leads from the battery terminals, & shut off when power is removed.. switch is a press on/press off type so I presume that there is something acting as a relay on the pcb. I'm wondering if I could solder a jumper across the terminals to have it come on automatically when power is switched on?..I noticed some 2302, & one 652DHR transistor on the board..Which of these does the switching, & would anyone happen to have a pinout for the 10 pin 652DHR? Thanks
     
  2. Frankchie

    Frankchie

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    Nov 14, 2017
    Soldering a jumper across the switch will likely turn the unit on when power is applied, but without a schematic it's impossible to tell if that is a completely trouble free solution. IOW, keeping the switch permanently on via a jumper might have some adverse consequences.

    Alternatively, assuming a DC voltage and a single pole switch, an electrolytic capacitor across the switch terminals would act like a jumper wire as it charges up when power is applied and when fully charged would appear as an open circuit. Kinda mimicking a momentary switch. Of course you need to install the cap according to polarity. Without more information it's impossible to predict the capacity value needed, but probably the biggest value that fits in the space would be a good starting point. You might have to install a resistor across the cap to bleed off the charge between power cycles. The higher value the better to avoid any potential circuit interference.

    BTW, are you sure that simply leaving the unit on between power cycles does not work?
     
    Harald Kapp likes this.
  3. outinthewoodsnf

    outinthewoodsnf

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    Nov 30, 2020
    Yes, it shut's off when you take out the batteries, and when you put the batteries back in, you have to press the power button to get it back on.... I was thinking that one of the components would be acting like a relay, with a power in, a power out, and a trigger terminal.... That's why I thought I may be able to bypass it by soldering the power in pin to the power out pin.
     
  4. Frankchie

    Frankchie

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    Nov 14, 2017
    What happens if you hold the power button down during power cycles? That might mimic your jumper solution and/or provide a "tape down the button" solution.

    Looks like the 2302 is a mosfet transistor that seems capable of doing the on/off switching. Of course, it could be serving a different function. https://alltransistors.com/mosfet/transistor.php?transistor=23894.

    The 652DHR is not a transistor since it has 10 pins. Anyway, I couldn't find any related technical information.
     
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Photos of the pc board? The power might be controlled by a microcontroller (what isn't these days?), making overriding its control program a bit more complicated.

    ak
     
  6. outinthewoodsnf

    outinthewoodsnf

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    Nov 30, 2020
    You solved it! Lol I can't believe I didn't think of keeping the button pressed in.... Talk about overthinking it! thanks! :)
     
    Martaine2005 likes this.
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    2,749
    Nov 17, 2011
    This modification may seem handy to you. There is, however, a reason this isn't designed as you want it to be but rather requires the switch to be operated: SAFETY.
    As with many other dangerous machines the design goal is to explicitly not activate the laser when power is applied to avoid risk of damage to other persons who may be endangered by the sudden and unexpected operation of a machine (laser) when power is applied. When the activation via a switch is required, this a conscious act and it can be expected that the operator is aware of the resulting dangerous action (here: laser beam) and has cleared the work area so no damage will occur.
    If the laser turns on immediately when power is applied, chances are that a person may be in the way of the laser beam an damage can result when the laser beam hits this person's eyes.
    For this reason special zero voltage safety switches are commonly used for machines like e.g. circular saws.

    In the light of this reasoning you may want to think twice before modding your laser.

    Regards,
    Harald Kapp
     
    ratstar likes this.
  8. outinthewoodsnf

    outinthewoodsnf

    6
    1
    Nov 30, 2020
    Thanks, but this laser is to be used for a totally different purpose than it was designed for
     
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