using a momentary switch and logic "And" chip

[kipper2k]

Hi all,

i am trying to create a simple circuit so that when i press a momentary switch with 5V on it it will cause a logic chip to output 5V and remain on once the momentary switch has been released.

Heres my thoughts, Take an "And" logic chip, feed one input with 5V continuous, and the other input wired to the momentary switch with 5V on it. pressing the momentary switch sends 5V to the other input and will cause the "And" chip to output 5v. Feed the output back to the (momentary switch) input of the "And" chip so once the chip has gone high then hopefully it should remain high until all power is removed, ie, computer shut down

I could then use the 5v output in my main circuit as a control voltage.

I dont have any logic chips on hand to test this theory.

Any thoughts ?

[Photon]

I guess you've already decided on using a momentary switch even though a normal switch to +5V through a resistor should do what you want.

Me, I'd just be lazy and use a latch http://en.wikipedia.org/wiki/Latch_(electronics)

Remember that different IC families have different foldout (5-20 or so). So you usually can't drive a bus or port with a simple AND chip, let alone power even a LED with it.

[kipper2k]

Thanks Photon,

This is what i am trying to do. I have a 27c800 EPROM with 2 kickstarts on it. I am looking for a way to use the momentary switch, (which is really tiny and low profile so it can't be accidentally flipped, knocked etc). I have quite a few of these that i salvaged from old floppy drives so i'd like to play and also put them to good use. These little things can be easily placed so they are accessible and look a little tidier than a toggle switch

So heres what i hope should happen...

- Turn on A600 normally and it boots KS 3.1 (lower 512K memory of the 27C800)

- Turn on computer while holding momentary switch, switch can be released as soon as the computer sees 5v. the 5V is tied to the high address line on the 27C800 and will remain high causing the upper 512K of menory (KS 2.05) in the 27c800 to be accessed until computer powers down.

[Shadowfire]

Its a simple holding circuit. Be aware that you need a pulldown resistor on the 2nd input to the AND gate (10K to ground should be sufficient) to make sure it powers up in the correct state, and a feedback resistor (~330 ohms) between the output and the input to limt the current when you push the switch, as you are shorting the AND low output directly to VCC when you press the button.

[kipper2k]

Originally Posted by Shadowfire

Its a simple holding circuit. Be aware that you need a pulldown resistor on the 2nd input to the AND gate (10K to ground should be sufficient) to make sure it powers up in the correct state, and a feedback resistor (~330 ohms) between the output and the input to limt the current when you push the switch, as you are shorting the AND low output directly to VCC when you press the button.

Excellent,

Thanks Shadowfire

[RedskullDC]

Hi Kipper2k,

Originally Posted by kipper2k

Hi all,

i am trying to create a simple circuit so that when i press a momentary switch with 5V on it it will cause a logic chip to output 5V and remain on once the momentary switch has been released.
...
Any thoughts ?

Turning the machine off/on to select the ROM version would be a nuisance.

Suggest you use a 74LS74 flip-flop.

Tie the CLOCK input to the Amiga's *RESET line.

Wire *SET and *CLEAR both to 5v.

Wire your momentary switch to the 'D' input.

Use either the Q or *Q outputs for your high address bit on the eprom, depending on how you have burnt the kickstart images.

When the machine is turned on, or reset, at the rising edge of the *RESET signal, the 'D' input will be sampled.
The flip-flop will stay in the same state till the next reset

Hope this helps,

Red


Fil

[kipper2k]

Thanks Red,

I'll try this out too.

Thanks

edit. there are a few out there, is this the correct 74ls74 below. I see there are also some with a preset. looks like the same circuit can be achieved using 2 Quad input Nand chips (which i do have kicking around). oops never mind, they are all 3 input Nands on the 74ls74

http://www.datasheetcatalog.org/data.../SN74LS74N.pdf