Page 2

Page 3

Page 4

Gecko G540 info

The Gecko G540 is a great device in that it crams an amazing amount of functionality into a very small space. This is some otherwise undocumented information about the G540 (and the four G250 drives buried inside) that I've learned since I've been using it:

1. The inputs, including the estop switch (pos 10 on the connector) are already despiked for noise and debounced for switch issues. Despiking capacitors on inputs to ground are not necessary.

2. The "power" LED on the front of the unit is kind of misnamed - it is more of a "ready" light that is only on if and when the fault light is off. If you have power applied correctly, one but not both of the LEDs should be lit. Kind of like a stop n go light - red means stop, while green means go. Also, inside the box, each of the 4 G250 drives have a separate red LED that is on when power is applied. Actually, these LEDs are part of the voltage regulator for each drive as well.

3. There is a switch on the G540 to turn off or on the requirement to have a "charge pump" present. On models made after May, 2009 the switch is external on the lower right hand side of the front cover. On earlier models, the switch is buried inside the unit, right next to connector pos 12.

This "charge pump" is an odd name for a watchdog timer - i.e., so that the G540 can tell if the computer is still running as it should, it needs an occasional (12,500 times a second!) nudge from the computer to tell it that Mach 3 is still running, and hasn't gone off to lala land. This name probably reflects the idea that the computer's constant pulse keeps a capacitor/semiconductor charged up to a particular voltage, and the 540 faults if it ever drops below that. Of course this means the computer has to spend beaucoup instruction cycles just to keep it charged up, but it does provide some protection that the computer hasn't lost its thread.

The switch has 2 positions - "charge pump required" or "charge pump not required" - the units normally ship with the switch in the "charge pump required" position, which is with the slider moved towards the center of the board. The later rev labels the switch "on" (required) or "off" (not required.) The documentation kind of says the only thing you need to do to get out of fault mode is to apply power and ground, and ground out pin 10 (i.e., connect a normally closed Estop switch to it.) However, you must also have the parallel cable plugged into the PC and Mach3 running and configured for a charge pump to get the fault condition to go out. On the newer models you can just flip the switch to remove the need for a "charge pump" signal, and you don't need the PC hooked up at all to get out of fault condition.

4. If the polarity of the power supply is reversed, or if you switch the DC side of the power supply, instead of the AC side, it will blow a very fast acting fuse in the unit. This fuse looks like an unstriped 1/2 watt resistor (actually it is a 0.04 ohm 2 watt resistor) and located just under and to the right of connector pos 12. It appears to be soldered, but on very close inspection it is actually socketed.

5. The G250 drives are interchangeable. If there is something wrong with any of the G250s, the fault light on the G540 will not go out. However, you can remove all of the G250s and plug them in one at a time (with the power off, of course, and then once plugged in apply power) to see which one may have the fault. This especially useful for troubleshooting if you are only using 3 of the axes anyway.

6. All the outputs are gated with the fault condition. This means that if the unit is or goes into a fault, the outputs are turned off. It also means that when the power is applied to the computer and the G540, the outputs from the G540 are dead until Mach 3 is running and providing the 12.5 kHz "charge pump" signal. This is good, since PC parallel ports are notorious for coming up with the pins in an undetermined state. It is one of the reasons you should enable the use of the "charge pump." You don't want your router to turn on just because the system is booting!

7. When the Estop switch is flipped (i.e. the Normally Closed circuit is opened) it causes a fault condition, which shuts down the steppers, turns on the red fault LED, and brings pin 15 (the Fault signal) high, telling Mach 3 a fault condition exists. Same thing if the charge pump fails. There is no need to route the Estop signal to both the G540 and the PC, just routing it to the G540 is enough.

8. If you need to open the G540 case (like to remove the need for a "charge pump" on the earlier models, or replace the fuse) be very careful as the case fits together very tightly. Make sure all the pins that are between the motherboard and each of the G250 drives are straight and apply an even downward pressure while keeping the two sides parallel to each other when reseating them. Stop about halfway down and make sure the green and red LED lights for "ready" and "fault" are also lined up for their holes properly, or damage may occur.

9. Geckodrive is an excellent company to do business with and have been quite responsive. I recommend them highly as a vendor, and I have no connection with them other than just being a customer.