Using diodes to protect a board

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mr aize
 
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Using diodes to protect a board

Post by mr aize »

Hello all. I'm planning on building an arcade cabinet, using a second hand motherboard but I want to install extra connectors in order to use it with various consoles. The idea is to loop over from the motherboard, to the controls in the cabinet, to a dsub connector and from the motherboard, to a scart plug, to the monitor. This would mean I could connect say, a megadrive, to the connectors and use the controls in the cab to play it. The problem, though, is that there will be a path, from the controls, back to the motherboard and so it could potentially get damaged. In order to work propperly, I won't be able to power the board, when playing the console. Anyways, down to the final question, if i installed schotky diodes, in line between the board and the controles and the board and the scart, would that protect the board, when it wasn't powered? Alternatively, is there some kind of multipole switch I could use? Would have to be capable of isolating at least 21 ways. Thanks.

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dr. au-fait
 
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Re: Using diodes to protect a board

Post by dr. au-fait »

For the power that would work provided the minor drop from the Schottky isn't a problem for any regulated voltages. I'd be really surprised if the data/signal lines continued to work with a diode in the path.

Maybe an array of p-channel MOSFETs would deliver a similar level of protection while still allowing the data lines to function? Probably depends a lot on the type of signals in use and I'm not familiar with most of what you mentioned there.

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neutron spin
 
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Re: Using diodes to protect a board

Post by neutron spin »

You could use optocouplers but that would increase the component count....why do you need isolation or protection for these lines?...also what type of signals will be travelling down the lines?...perhaps I am reading your post wrong...regards...

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chatham
 
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Re: Using diodes to protect a board

Post by chatham »

Would it make sense to have some sort of connector that goes between your controls and your JAMMA harness or whatever connector you've got for your board? Then when you want to use the controls to play other systems, you can unplug that and plug that into your other system. Just a thought.

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zener
 
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Re: Using diodes to protect a board

Post by zener »

If you are trying to protect from ESD (not a bad idea) then the best way probably is clamping diodes to your supply rails, and/or some zeners/transorbs to ground. There are also specialty parts and arrays made for this purpose, for example from Littelfuse SP720, SP721 etc.

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mr aize
 
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Re: Using diodes to protect a board

Post by mr aize »

Thanks everyone. Right, firstly, gonna have to mention that my electronics knowledge is fairly basic so appologies if I get confused...
I like the idea of mosfets (mostly because i can get my head around them) but wouldn't n types be easier? I can easily get the +5 from my jamma harness to operate them so, when the board is powered off, they will be off and provide the required protection? I'm afraid I couldn't find anything on p types so I could be getting confused but it looks to me, that in those, the gate is permanently closed, (allowing current to flow) unless a negative charge is applied?
I did consider using a connector, between the harness and controls/scart but it would mean having to open the cab every time I wanted to play something different and I really wanted to have the simplicity of a switch.

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zener
 
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Re: Using diodes to protect a board

Post by zener »

Hmmm... Well I will say for the record I don't know what you are trying to do.

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mr aize
 
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Re: Using diodes to protect a board

Post by mr aize »

To be perfectly honest, i'm not entirely sure myself :lol: I just want some way of isolating all the connections between the arcade motherboard and the controls/monitor without having to physically unplug anything. I'm afraid my electronics knowledge is limited to what i've picked up by myself so shakey at best... My understanding (probably wrong) is that an n type mosfet only allows voltage to pass, when 5v is applied to the gate, therefore, when the board was not powered and so not supplying the 5v, it would not allow any voltage to pass and provide the isolation I want.

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