Main Site Documentation

ReleyISOx16 default state of relays without control signal


#1

If I supply 12VDC to the RelayISOx16 and don’t have it hooked up to my spider, all the relays come on. Is there a way of changing this default condition? Basically if my spider fails, it’s going to act like I turned on everything, which seems completely backwards. I would think default state would be “off”.

Right now having an issue with turning on solenoids. As soon as I have one hooked up and turn it on, all the relays clack on. If I don’t have the solenoid connected, the solenoids turn on and off as expected pragmatically. Headed to the store to pick up some diodes to hopefully take care of the solenoid issue, but the back of my head is worried about what happens if my control system goes black, suddenly every solenoid would turn on and do something entirely nasty.


#2

The documents for the board are very sparse and only shows the schematic for the small header module and nothing for the relay board itself.

Looking at the input to the relay module, the inputs are active LOW and it looks like the 74HC595 is powering up in an unknown state when nothing is connected and they are likely in the LOW state or floating close to it.

I would save, the fault lies in the design of the relay board itself as it should have pull ups on the inputs to the drivers to prevent this. As in most cases it would be connected to a microcontroller which has IO in the default INPUT state on reset, this would prevent the relays from switching on.

When I design with relays, this is how I make sure the relay is always off during power up.

There is a MR input to the 74HC595 that could be tied low with a resistor but this will only set the outputs to LOW, which again will fire the relays.

I can’t make out the details on the relay board, but could you put PULL UPS on the driver outputs?


#3

Good question. We will check if there is a way to handle this.


#4

We looked into it and we found that the relay should not be powered without the mainboard being connected.


#5

I’m not understanding. If I supply 12VDC without anything being connected to my RelayISOx16 board, all the relays light up red. Does that mean there is something defective with my board?


#6

If I have it connected to my spider and the spider is on, none of the relays come on until I expressly send the command(minus issues I’m correcting with diodes)


#7

Having spider connected to the relay module is required. This goes for any module and any mainboard.


#8

Once the power to the spider goes dark, all the relays light up, that’s my issue. If something goes wrong with the spider or the power supply to the spider, everything will go ultra wacky.


#9

Sorry…already going wacky. When we remove the power to the machine, the relays trip for the a moment and causes all our solenoids to open up. Since one of them is a clamp, this causes it to drop things. Normally this clamp remains closed and another solenoid releases air from the system slowly when the power is removed so it can be manually opened if necessary. This whole -pop- thing is a problem. I’m not sure if I can put a capacitor on the power going to the spider so it can slightly outlive the relay board or what.


#10

It is best if you power the mainboard and the relay from same power source.


#11

They are. Shutting power off to the power supply causes the relays to flash on for a brief period.


#12

I’ve sort of worked around this by buffering the exit air valve on the most critical air solenoid so it takes longer to open. But it’s still a worrisome condition.


#13

Gadgeteer is a prototyping system. GHI has never said that the modules are ready for production devices.

I believe there are special chips made for handling power-up issues like you are experiencing.


#14

This device uses 74 Series logic chips (74HC595 specifically) so without mods you’re unlikely to be able to externally influence the output lines that go to the relays when the power goes out to those chips. But if you were turning this into a real production device you could add pull-downs or pull-ups to control the default behaviour when power was applied.