"Is Blowing" Relay

Discussions and help on this commercial controller.

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"Is Blowing" Relay

Postby bdring » Fri Oct 14, 2011 12:45 am

Thunder Laser sent out a few relays to some 2.x folks. The relay attaches to pin 3 on the I/O terminal block. The relay is sync'ed to a running job. You can use this to run your assist air whenever you run a program, for example.

This is the relay that they sent to me.

thunder_relay.JPG


I thought it was a really nice option, but I had a few issues with the this board that made me decide to roll my own solution.
  • I really did not want to mount another device to my electronics module and the wiring looked simple, but busy.
  • I am not a big fan of these little relays. I prefer DIN rail versions that are cheap (<$10), easy to replace and resize.
  • I don't like the +5 and Input (AC) on the same terminal block. I am sure it is fine, but in addition to running an Engineering department I also run a PCB layout group. We deal with a lot of international safety agencies and I know this would not meet UL or CE creapage and clearance rules. I am sure it is fine for DIY use, but old habits die hard.

The relay is rated for 240 VAC, but you could use this to fire a DIN relay using 24V if you are concerned about the safety issue I mentioned.


I did this simple little mod to my 4 axis controller. I made a little Pololu compatible relay driver. This uses the same signal to fire a 24V DIN relay. It really makes a clean setup because all the voltages are already on the driver board. It is one wire (bottom white wire) to the Thunder Laser DSP and 2 wires to the relay. I will probably have a bunch of these boards made. I only partially stuffed this board for initial testing. I will probably put two drivers on this board (one on step and one on the dir signal)

When you power up the laser, the relay engages right away. Since the relay is form C contacts (SPDT), you can put the device under control on the N.C. side. When the job runs the relay disengages which can turn on/off your device.

The feature is control using the "Is Blowing" check box on the Manufacturer Settings page. This is nice because I don't always use air, like on glass jobs or anodized aluminum. I don't like the noise.
dsp_relay.JPG
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Re: "Is Blowing" Relay

Postby naPS » Fri Oct 14, 2011 2:24 am

Is the output on the board 5vdc? I was under the impression that it was 24vdc.
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Re: "Is Blowing" Relay

Postby bdring » Fri Oct 14, 2011 2:35 am

Is the output on the board 5vdc


I am not sure what board you are talking about. There is a good schematic of the circuit in the Thunder Laser documentation on the Wiki. I assume the controller outputs a TTL signal on "wind". If it goes high, the transistor will conduct to ground and energize the relay. The relay has a 5V coil and the contacts rated to 240VAC @ 7A or 120VAC at 10A.

isblowing_schm.JPG


My circuit is very close to the Thunder circuit, except the relay is off board and I have a 10k pull down in front of the transistor in case the circuit is left open. I use 24V instead of 5V to drive the relay because that is a standard voltage for DIN relays.
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Mine does not work

Postby J45on » Fri Oct 14, 2011 1:14 pm

I have the board and have wired it correctly but my relay fails to switch over
My "wind" pin on the DSP I/O port has 5 volts constant but only drops to 2.39 volts when running a job I presume this is why it does not work :?
Should it drop to zero volts ?
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Re: "Is Blowing" Relay

Postby bdring » Fri Oct 14, 2011 1:24 pm

I actually did not try their board.

It should drop to TTL low. That is usually 0V to about 0.8V. The only difference is my circuit has a pull down of a 10k Ohm resistor. It is possible that there is not enough load on the signal to pull it down. Without knowing what their controller circuit looks like it is hard to tell. It can't hurt and makes the circuit more robust if the signal is gets disconnected.

It will be real easy to add. Just put it across wind and ground on the relay board terminal block. Any value resistor between 5k and 20k should do with 10k being the standard value.
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Re: "Is Blowing" Relay

Postby J45on » Fri Oct 14, 2011 1:29 pm

Thanks Bart I shall go and try that now :D
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Re: "Is Blowing" Relay

Postby J45on » Fri Oct 14, 2011 1:45 pm

Hmm no luck with that I used a 1/2w 10k Ohm resistor
I now get ( without the relay board connected) 4.55 volts and 2.18 volts when running a job :?
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Re: "Is Blowing" Relay

Postby bdring » Fri Oct 14, 2011 2:14 pm

I also have a schmitt trigger in the circuit. I use a schmitt trigger to create a much sharper High/Low transition and add some hysteresis. Hysteresis is like an overlap of the high to low and low to high transisition. For example, it might need to go to 3.25V to be a high, but then needs to go below 2.75V to go back to low. This prevents a signal from sitting at a transition point and jittering between them.

This is like a snap action micro switch. It snaps cleanly from one state to the other without a point where it can easily move between with little mechanical movement.

Anyway, enough science class, bottom line....my low state is probably a lot higher than yours. Are you using any of my PCBs? We may be able to tap into them and fix your problem.
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Re: "Is Blowing" Relay

Postby J45on » Fri Oct 14, 2011 3:58 pm

I am using your "Laser Interface/Driver PCB" if that helps
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Re: "Is Blowing" Relay

Postby bdring » Fri Oct 14, 2011 4:27 pm

That one won't help you much....no easy spare schmitt gates I'll send a note to Thunder asking them. You could try using a couple resistors or a pot to divide the voltage down.
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