Detonator card, looking for advices.

Hi,

Attached here is the schematic for a detonator card I'm planning to build to interface it to the Arduino. It's fairly simple I think : A 2x5 pins HL-10 connectors brings 8 line, as follows :

1 : +5V VCC
2 : GND
3 : Output code, bit 1
4 : Output code, bit 2
5 : Output code, bit 3
6 : Output code, bit 4
7 : Trigger, HIGH to start.
8 : Trigger, LOW to start. (Can be disabled)
9 : Unused.
10 : Unused.

You just send a 4 bits number through lines 3 to 6 then enables the power output by making line 7 LOW and line 8 HIGH. Thus, as the 74HCT154N puts the selected output at LOW, there's an array of FET transistors to send power to the selected output.

The SW1 switch allows to disable the 8th line and make the system require only the 7th line to be HIGH to send power.

There's an additionnal power input, labeled 12VDCC-IN, which provides enough power to fire the igniters.

As this is my first "serious" electronics work, I'd like to get a few advices before starting to make the PCB...The FET transistors reference is not the final one, I haven't yet taken the time to find transistors able to handle that much current.

A lot of thanks in advance for the courageous people who'll take the time to review my schematics and point me if I'm wrong at something (Not only just about circuit design, but also in the way it is graphically designed... Maybe I could have made it simpler)

(Of course, schematic and PCB layout will be released for free for anybody interested.)

Schematic is here : http://whiterabbit.disposition-worldwide.com/detonator%20card.png (Removed direct image link as it was too big and breaked out the forum's design)

make it controlled by a wii nunchuck =P

Is the 2n3819 a "placeholder" part used jst because it has an appropriat footprint? It's a depletion mode RF-frequency amplifier/mixer part, not really suitable to the high-current switching app that you're creating.

You are also using the fets as "high side" switches, which means that they'll probably need to be P-channel MOSFETs and will need some sort of HV gate driver; It's more common for this sort of App to stick an N-channel mosfet in between the load and GND (a "low side" switch), because that way the needed gate voltage is referenced to GND...

Is the 2n3819 a "placeholder" part used jst because it has an appropriat footprint? It's a depletion mode RF-frequency amplifier/mixer part, not really suitable to the high-current switching app that you're creating.

Yes, it is only a placeholder. I haven't searched for the right part, yet.

You are also using the fets as "high side" switches, which means that they'll probably need to be P-channel MOSFETs and will need some sort of HV gate driver; It's more common for this sort of App to stick an N-channel mosfet in between the load and GND (a "low side" switch), because that way the needed gate voltage is referenced to GND...

I don't exactly get this point. The 74HCT154N puts the selected pin at the LOW state, so I'm planning to use a N-Channel *FET or similar which (IIRC) let current pass between drain and source if gate is at 0V. Am I wrong at something ?

I think I also forgot to add a safety resistor between gate and source... Am I right ?

Sorry, my questions are probably quite dumb :slight_smile:

Thanks for your answer,
T.