1. ## V=I*R

Of all the trades I feel comfortable with, electronics isn't my strong suit. I've let the magic smoke out on more occasions than I care to tell. I need help fella's.

I'm in the process of setting up the zeroing laser on my machine. I've got the laser wired up to a 5 volt phone charger and done some rigging. Bottom line is can I power this thing using only the output voltage/amps from my G540 with no other relays or anything.

Specs of the laser:
New Red Laser Module - Adjustable Crosshair (3.5V~4.5V 9mm 5mW)

Specs on the phone charger:
5 volt, 550 ma

Total resistance of all the resistors wired in parallel: 72.7 ohms

Voltage before the resistors 5.05vdc

Voltage after the resistors 2.93vdc

HELP!

2. i'm in the same boat as you.. electronics are my weak point...

maybe take a few resistors out and try it again?

3. The laser is working perfectly with the above specs. I got the macro to work perfectly, (Thanks Ger21 for the 2010 screenset and TweakieCNC for his awesome right up) I just need to know if by looking at the specs I posted, can I use the output of my G540 to power the laser without any other relays.

4. You're given that the power dissipated is 5mW or 5 x 10^-3 Watts. Power equals Voltage times Current (P=E x I). On the low voltage then the current drawn by the laser is:

(5 x 10^-3)/3.5=1.43 milliamps.

On the high voltage the current drawn by the laser is:

(5 x 10^-3)/4.5=1.11 milliamps

The G540 appears to be able to output 50 watts of power (1 amp at 50 volts). See the spec sheet attached. You should therefore have no trouble powering the laser. You could even try to bring the voltage up a little bit higher into its specified operating range (3.5-4.5v) to get the best performance.

Chris

5. I do appreciate that but I just got more confused. If I'm reading the chart you posted correctly, the output is capable of 50vdc @ 1amp? I always understood the output of the G540 was approx 5v. I'm sure my ability to understand is off. Please clarify.

6. Ok maybe the 50v is the output for the motors and the 1A is the current output for the 5v. If that's the case then the 5v supply can source 5 watts of power so you're still ok regarding the laser. I couldn't find an input/output wiring schematic for the 540 on the gecko site. Do you have any specification in your documentation regarding the 5v supply pin? I'm assuming that because the g540 has its own BOB it has a 5v power pin. If I'm wrong about this and the 5v supply is coming from the computer logic signal then I don't know how much current that source can supply.

Chris

7. Originally Posted by OCNC
Ok maybe the 50v is the output for the motors and the 1A is the current output for the 5v. If that's the case then the 5v supply can source 5 watts of power so you're still ok regarding the laser. I couldn't find an input/output wiring schematic for the 540 on the gecko site. Do you have any specification in your documentation regarding the 5v supply pin? I'm assuming that because the g540 has its own BOB it has a 5v power pin. If I'm wrong about this and the 5v supply is coming from the computer logic signal then I don't know how much current that source can supply.

Chris

Ok, forget everything I've said. We need to start again. Where are you going to get the 5V from?

8. If you are dropping 2.12v across 72.7 ohms that means the current draw is .029amp or 29ma.
145 mwatts at 5v supply.
Al.

9. Originally Posted by IBBruin
Bottom line is can I power this thing using only the output voltage/amps from my G540 with no other relays or anything.
The 'Outputs' on the g540 are like switches that can be thrown by software to complete a physical circuit to ground. They are not 'Outputs' like you would find on a power supply that output a voltage or current.

It looks to me like the g250's that make up the g540 get their logic power from the single power supply that is used to power the motors. Internally to the drive there must be a voltage regulator that is dropping the input voltage (15-50V) down to the 5V logic level that the drives require to function. There doesn't appear to be any way to tap into this logic level voltage to power the laser diode. You will therefore have to use an external voltage source to power the diode. My apologies for the earlier confusion.

Chris

10. Thanks for all the replies. If the g540 can't power it, can I power it directly from a printer port pin?

11. Originally Posted by IBBruin
Thanks for all the replies. If the g540 can't power it, can I power it directly from a printer port pin?
By Al's calculation you need around 145 mWatts of power. Looking at info on the net it appears that you could get the power from the USB port but not the parallel port.

Chris

12. What I would do is use a 10˘ 2n7000 buffer off the printer port, and if necessary use the 5v from the PC power supply.
There are a few previous posts on using the 2n7000, no other component needed.
Al.

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