Switches

[Smoke2much]

I need some advice.  I am building a "panel" for a single engine GA aircraft to replace many of the keyboard functions.

I am planning to use a game pad and the guts of a keyboard to provide the functions.

My  problem is that I want some of the functions to be switches rather than buttons eg the lights.  How can I convert a button press to a switch?

For example if I assign "L" to the landing lights on a keyboard I press L and the lights come on.  If I solder in a switch to replace L when I switch the lights on it will be the equivalent of holding my finger on L and the lights would constantly switch on and off.

Any clues?

Will

[JBaymore]

Will,

I have been pondering this one too.

[Smoke2much]

Thanks John.  What I was thinking of doing was using the Keyboard buttons and cleaning the letter information off.  Each button would then run two of the press switches at the same time, the LED's would be on a seperate circuit and be battery powered.

Will

[Vchat20]

can someone plz either explain or redo that diagram in that article for me? im quite confused. what I dont get ishow the 10V source is supposed to temporarily charge the capacitor. might be better if you just explain the whole thing for me so I dont get confused.

[Smoke2much]

I'm trying to get my head around the diagram as well Vchat.  I haven't had to look at electronics for the best part of 12 years LOL.

The article states that you need more complex electronics to run Shift + functions or Ctrl + functions, I think it would be possible to run these by simply duplicating the diagram shown, one for each button.  Or make the circuit with two capacitors in parrallel, each running a separate relay.  The two relays should go off simultaneously giving you the response you need.  You could even run the Shift or Ctrl relay from a slightly larger capacitor so that the relay stays on for longer and gives the effect of holding down the button ensuring that it is picked up as a Shift +, and not a Shift then.

If you follow me.

Will

[Vchat20]

yeah, I follow you. so what you explained could be easily used as an engine cutoff switch if made properly.

this is all getting more confusing by the minute.  ???

[Smoke2much]

The great thing about the Home cockpit set up is that you can make it as complex or as simple as you like.  The great thing about relays is that one switch can be made to operate as many circuits as you want to.  With the Shift+ or Ctrl+ functions and an LED or light bulb you have three separate functions from one switch.  Nice.

Remember that a keyboard has 67 buttons on it

A-Z (26)

` [ ] ; ' # , . / \ Tab = - Backspace Insert Delete Home End Page Up Page (19)

Num Pad 1-0 (10)

Function Keys (12)

not including 1 to 0 which are hardwired to ATC functions. This effectively gives you 67 switches to play with not including any buttons that come from joysticks/joypads that you have cannibalised for potentiometers.

You shouldn't need to have any shifted functions.

Will

[Vchat20]

well, just sent an email to the guy with the toggle switch wiring page and hopefully I can get a detailed story on exactly how the thing is wired out of him. ill post any results I get here.

[HerSELF]

Thanks Vchat it will certainly clear-up the confusion in this house if you can.

Sarah

[Vchat20]

well, i got a reply. hope it helps

Hi,
Thanks for your remark. I'll try to reply, though I'm not too sure which part is the tricky one my site. If it is about wiring a relay or a capacitor, please let me know; I could send you some picture or PCB layout. If it is about how exactly this circuit works, then here we go:

Any relay consists of a switch (left part in the relay drawing on the webpage) and a coil (right part). When an electric current is running through it, the coil becomes electromagnetic and thereby attracts and closes the switch. As long as the coil current is strong enough, the relay switch remains closed.

While the capacitor is getting charged more and more by this current, the voltage over the capacitor increases. Hence the voltage over the relay coil diminishes, as the two voltages have to add up to 10 V, the external power source. With the relay coil voltage getting lower and lower, at some point the coil-current will no longer be strong enough to keep the relay switch closed.

In the end the capacitor is charged, its voltage 10 V, the current has stopped. The whole 'pulse' doesn't take more than some milliseconds.

When the main switch is toggled (from the 10 V position to the 0 V position) the capacitor starts to discharge, as it is connected to zero. The generated discharging current activates the relay coil and closes the relay switch. This 'pulse' won't last for long either: the capacitors voltage drops as it loses charge, the current diminishing proportionally.


I hope this will help. Otherwise don't hesitate to remail.

[Vchat20]

ok. i think I get it now. follow me through this diagram as best as possible:

what happens is when the switch is flipped to on, it connectes the 10V source (anything from a battery or sourced from a ac/dc transformer) to the rest of the circuit. this connects the capacitor (indicated as the break in the circuit with the label "220uF") to that source and charges it. as the capacitor voltage rises up to 10V the current slowly drops. while it is doing this the relay has already done its work and has activated the keystroke. when the capacitor reaches 10V, there is no longer enough current left to operate the relay. the relay then stops the keystroke. the toggle switch is still in the on position but the key is no longer being pressed. when the switch is flipped to the off position, it connects both sides of the capacitor to the 0V source and thus it discharges. when this happens the current is then back to normal and activates the relay once more. and with no electrical source to charge the cpacitor slowly loses al its charge, once that happens the relay stops working again and the keystroke has ended. anyone understand now?

btw, the extra bit with the dashed lines is just showing how to connect a LED indicator to the circuit. the long rectangle part is a resistor and  the part below it is the LED.

[JBaymore]

Vchat,

You have the idea fundamentally correct.

Just to clarify a tad..... it is the electrical charge stored in the capacitor when it was connected to a positive voltage source that activates the relay as it discharges to the ground (0V) that the switch connects it to when in the "off" position.

This is a pretty simple solution to the "constant keypress" problem.

BTW..... nothing magic about the 10V+ figure.

[Smoke2much]

Neither will the capacitor circuit.  You need to switch it "on" each time to get a key press.  The only way I can see of working stuff with switches is by having three position jobs.

ON
OFF
ON

You would have to push the switch through the off section for each toggle of the "key" relay.

Things are on hold until I get the use of my left thumb back. Stuck a knife in it.

Will

[KnightStryker]

[quote]Things are on hold until I get the use of my left thumb back. Stuck a knife in it.

[JBaymore]

[quote]Neither will the capacitor circuit.