Autofire Joystick project.

Modern, Memotech inspired, hardware projects
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Crazyboss
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Autofire Joystick project.

Post by Crazyboss »

Hi.

I wanted to build an autofire for the MTX. I tried to use the 555 timer ic.

But it seems like the 555 timer do not put out a very square output, and that fools the MTX to think when its not firering, other inputs come to the joystick.

Some people suggested to add a npn transistor, at the output.

I dont know if its save to use an external power source for the 5v, as i do, or there is another way to do it, I plan to build it into my multi joystick, so was thinking to add a usb port for powersourch for the autofire.
555 timer.png
555 timer.png (93.29 KiB) Viewed 144 times
Any suggestions, I would like to make the autofire variable so it can be adjusted.
//CLAUS - Webmaster at www.mtxworld.dk
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1024MAK
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Re: Autofire Joystick project.

Post by 1024MAK »

The problem with the joystick ports on the MTX is that they are part of the keyboard matrix. The keyboard matrix does not use a 0V common but is instead a grid where the system controls the voltage on one set of lines (outputs) while monitoring the logic level on the other set of lines (inputs). By using a process of using different logic levels on the outputs, the system can work out which key or keys are pressed, while using the minimum amount of hardware.

So you can’t use a NE555 or a simple transistor output circuit :(

What is worse, is that the two joystick ports use very different parts of the keyboard matrix, so it’s not easy to design a suitable simple transistor circuit that will work in both joystick ports :(

However, there are analogue electronic switch chips and opto-couplers available.

Which joystick port is your preference, and do you need the adapter to work in just this port or in both of them?

Mark
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Crazyboss
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Re: Autofire Joystick project.

Post by Crazyboss »

Hi Mark. Thanks for the input.

But if there was a chip somthing like a relay, which could be driven by the 555, so it could open and close just like a manual push button do it would be perfect I was told a NPN could do that, but its not the case. Maybe it works for C64, Amiga etc. But not for MTX.

So if there was souch a chip or something that dont share gnd, actually i think a old fashion relay could be used right ?
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1024MAK
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Re: Autofire Joystick project.

Post by 1024MAK »

There are chips that can be used, for example CD4016BE or CD4066BE analogue switches.

CD4016BE datasheet from TI
CD4066BE datasheet from TI

Use the output of the NE555 (or 7555 or TLC555CP) to feed one of the control inputs on one of the switches/channels of the CD4016BE or CD4066BE chips. Then connect the two switch/channel pins across the joysticks fire button contacts.

I recommend using a 5V supply from the MTX. But if you use an external supply, the 0V/GND of this supply must connect to a 0V/GND on the MTX somewhere. Otherwise any difference in ground voltage will kill the CD4016BE or CD4066BE chip.

It’s also a good idea to connect a 100nF ceramic capacitor across the supply pins of the CD4016BE or CD4066BE and if you are using the NE555 timer chip, that needs a 47µF to 100µF electrolytic capacitor across the supply pins of this chip. If a 7555 or TLC555CP is being used, this can be reduced to a 10µF capacitor.

Also looking at the circuit you posted for the 555, I strongly recommend wiring a 470Ω resistor between the +5V supply and the pot/variable resistor.

Mark
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Re: Autofire Joystick project.

Post by Crazyboss »

Mark, i tried another circuit today.
555 timer.png
555 timer.png (66.74 KiB) Viewed 123 times
It worked great, I made a test program (in basic), it seems like i can manual shoot around 15-20 shoots per second.

The relay seems to give up around 15 shoots per second.

Maybe a solid state relay is faster, i used the click one.

acutally my test program shows the relay can shoot faster than 20 shoots per second, but then the relay stop clicking, but maybe it so fast so we dont hear the click.

the game we played at memofest 2019, at Andys home "Exoide-Z", seems to like 10-11 shoots per second, for optimal shooting.

Image
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1024MAK
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Re: Autofire Joystick project.

Post by 1024MAK »

Sounds like you’re have fun :D

Smaller electro-mechanical relays are faster than larger ones.

Beware that the ‘back EMF’ (a voltage spike) generated from the real coil when power is removed from it can damage semiconductor devices that drive it. A fast diode (1N4148 for small relays, UF4001 for larger types, or 1N4001 if you don’t have anything better) wired in reverse across the relay coils (cathode to positive or equivalent, anode to GND or equivalent) will protect against this. But the diode will slightly slow dow the relay de-energizing.

Mark
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