Guide - Simple & Cheap standalone electronic solution for single pull ejection

[Scott-S6]

The problem - DCS requires the ejection command (button or keystroke) to be triggered three times for ejection to fire. This sucks for people that want a proper ejection handle because you definitely don't want to be pulling on it three times to get an eject.

The other solutions - there are definitely other solutions to the problem, the two most commonly suggested are:
Software - there are apps that will make joystick buttons pulse. If you're using one of these apps for something else then great. If not, adding an additional app just for this isn't a good solution in my opinion. Minimizing the amount of crap running in the background is a good idea generally.
Arduino - definitely a viable solution but total overkill on cost and complexity if you're only using it for the ejection handle. If you've already got an Arduino in your cockpit doing other things then you should definitely go with that (but you probably just did that rather than searching and finding this guide).

This solution - we're going to use a 555timer circuit (bought as a pre-assembled package) as an oscillator to make a relay flap open/closed triggering repeated button presses while the ejection handle is pulled. I know that sounds kinda complicated but it really isn't. No knowledge of electronics required.

The disclaimer - I'm assuming that you can strip wires and join them together (soldering, terminal blocks, crimped connectors, whatever - I don't judge). If you aren't sure that you can do that then this is not the guide for you. Learn how to do that first. I am also assuming basic electrical knowledge. Don't go hooking this up to the mains and then blaming me when your house catches fire.

High-Level design

This is how it's going to work:

Power source (for this guide, USB power)
to
Switch in the ejection handle
to
555 board
to
Relay
to
Button Board

When we pull the handle the switch connects the 555 timer board to power. The output of the timer board pulses on and off which causes the relay to open and close. The relay's output is connected to the button board so registers as a button press in game.

Things you'll need:
USB Cable
Switch
555 board
Relay
Button Board

(note, I'm referencing prices below in USD because that's easy for most people to relate their local currency to.)

USB Cable - There are lots of things you could use for power but I'm going to go with USB for this guide. That means you need a USB hub (if you're building a cockpit I'm sure you've got a pile of those) or you could use a USB charger, since we only want power, which I'm also sure you have lying around. You also need a USB cable with one end suitable for your hub/charger. Ideally, use a power-only cable (only two wires). You could just ignore the data wires but I dislike having data wires floating around not connected to anything just in case they get shorted on something.

Switch - This is a low voltage, low current application so any switch will do. The design of your handle mechanism is going to determine the type of switch you need. I went with a magnetic switch, the type used by security systems to tell if a door is open or closed. They're very cheap, $2-3 for a pack of 10.

555 timer - You'll find these extremely cheap on AliExpress and similar. Expect to pay $1 for the unit and $2 for shipping or thereabouts. There are lots to choose from but there are a couple of things we're looking for. We want 5V to be within the range of the input voltage offered and we want one of the frequency ranges to be suitable. What's suitable? We want ejection to go off in a fraction of second but we don't want the button to be getting pressed thousands of times a second or it'll get rejected as erroneous data. 10-20 times a second is perfect so we want 10-20Hz. The unit shown in the pic has 1-50Hz as one of the frequency ranges so that's perfect.

The 555 board looks complicated but it's really not. Key things to look at:
The jumper with four positions, that's where we pick frequency range. Make sure it's in the 1-50 (or whatever your's has that is suitable) position.
The frequency adjustment screw, we're going to turn that to make the on/off faster or slower.
Indicator light, not essential but useful for troubleshooting.
VCC - this is where the 5v from the USB goes
GND - this is where the ground from the USB and from the relay coil go
OUT - this is where the other side of the relay coil goes

Relay - The only things we need to worry about here are that it's a 5V relay (5V and 12V are the common voltages) and that it's small. I paid $3 for one domestically but they're much cheaper bought import (if you want a few) We don't want a beefy relay because it will take more power to run the coil and our 555 board may not be up to it. My relay is a 10A max output and it's nominally too much for the 555 board but it works fine. Definitely don't go bigger than 10A

Lots of pins on the relay but the diagram explains it for us.
Pins1 and 2 are the electromagnet. We're going to connect them to GND and OUT on the 555 board. Doesn't matter which way round.
Pins3 and 4 are connected when the electromagnet is powered so we'll connect them to our button board. Doesn't matter which way round.
Pins3 and 5 are connected when the electromagnet is NOT powered. We don't need that here but I mention it in case it is useful to someone for another project.

Button Board - there are lots of these and I'm going to assume that as a cockpit builder you already have one. I like the ones that Leo Bodnar makes but use whatever you prefer.

Total cost for these parts (assuming that you have a button board and a USB port) = ~$10

This is how everything hooks together:
Red = positive
Black = ground
Blue = doesn't matter
This does not indicate what color your wires will be. If you cannot look up the colors for the USB cable or use a tester to verify them then, again, this is not the guide for you because you should have basic electrical knowledge. 

And that's it. All you have to do now is tune the frequency adjust screw to something which gives you an acceptable delay between handle pull and ejection.

As is mandatory, here's what mine looks like. You can see that I've used a piece of plastic board to isolate the circuit board from the metal panel and to keep the 555 board, relay and cable anchors together. You could, of course, put this into an enclosure but I like having easy access. YMMV.

And here's the handle itself. Before anyone asks, the wire loop is a real martin baker part (they aren't expensive because making the metal block that the ends plug into is a bit of a hassle. Filing square internal bores isn't fun. If you have a rotary broach then you'll find it rather easier). The high position is because I fly sidestick, I based the handle position on the Rafale.

EDIT - pictures now attached rather than linked.

 

 

 

 

Edited July 13, 2023 by Scott-S6
image edits

[Baldawg]

Could you post links to the timing circuit and relay.  I'm looking for the exact one you are showing in the diagram but I'm having trouble finding them.

[No1sonuk]

That relay should have a diode reversed across the coil pins to protect the 555 input from back-EMF spikes.

Also, did you try connecting the output of the 555 module directly to the Bodnar board input?
If you use a common 5V power supply (i.e. power the 555 module from the Bodnar board), it might work without the relay...

[Scott-S6]

Here's a link to that particular 555 unit but there are lots that are suitable.

AliExpress link

If you aren't in the UK the relay link won't be very useful to you. 

eBay link

Virtually any 5V relay will do, 10A switched current or less (the lower the better). Get whatever relay and if you're not sure about the pin layout post a pic and I'll explain how to read the diagram.

 

Given the very low voltage & current at play together with the low frequency, back emf isn't really a concern here but it certainly wouldn't hurt to stick a diode on if you wanted.

Leo's boards use 3.3v for sense voltage. It'd probably work if you skipped the relay, they're pretty resilient boards, and you could throw a resistor in there to drop the voltage but it's a potentially messy scenario that can be completely avoided with the relay.

Edited May 3, 2022 by Scott-S6

[Gruman]

Another simple hardware way would be to simply use 3 buttons in a row (connected parallel to the same I/O Port), which gets activated with the pulling motion. You get 3 button presses, which "should" trigger the eject reliably. But of course you would need some travel distance for the ejection handle action.

[Scott-S6]

The trick with three buttons is that you have to ensure that the actuated switch is reset before the next is actuated. The timing of that is important. Or, you could have a saw tooth arrangement that presses the same switch three times during the ejection handle stroke.

Both a bit messy imo. The electronic/software/programmable solutions all leave the handle mechanism extremely simple which I think is desirable considering that it needs to be pretty robust.

[No1sonuk]

4 hours ago, Scott-S6 said:

The trick with three buttons is that you have to ensure that the actuated switch is reset before the next is actuated. The timing of that is important. Or, you could have a saw tooth arrangement that presses the same switch three times during the ejection handle stroke.

Both a bit messy imo. The electronic/software/programmable solutions all leave the handle mechanism extremely simple which I think is desirable considering that it needs to be pretty robust.

I made the attached drawing for a post here almost 2 years ago.

[Scott-S6]

10 minutes ago, No1sonuk said:

I made the attached drawing for a post here almost 2 years ago.

Yep, that thread was one of the ones that I went through for research before building my ejection handle.

[Scott-S6]

Quick update to say that this solution is still working great two years on. No issues with the longevity of the 555 board, relay or mag switch.

Also, updated handle pic.

Edited April 26, 2024 by Scott-S6