options switching

[steve100]

Having looked at the suggestion for wiring the options switch using the 1k resistor, I’d prefer to do it slightly differently.

I suggest doing (as suggested) in replacing L1 with the 1 k resitor but using that as a permanent 5v pull up onto the Option line. This could be done very simply by connecting the Option and VREF feeds at the socket where they come off the board and into the socket.

Then you can use a single wire from the option line plug to pull it down to 0v when the alternative configuration is required.

That means you only need one wire from the megajolt to a remote SPST switch to pull Option down via a remote earth point to operate/switch configurations .

Would this work ok , especially wrt having the shunt load pulled down to 0v for long periods & with this in mind in order to minimise the load would it be better to use say a 5k or 10k pull up resistor at L1 to minimize shunting current load.

Thanks
Steve

[brentp]

Hi Steve,

Yes, if there was a "modify your board" option for enabling the option switch, this would be best. Using a 1K resistor for the pull up would only consume 5ma of current, which is trivial. You should be fine.

It seems we should update the wiki with this suggestion!

Regards,

[MartinM]

Also probably better as with the two wires to the switch version, there could be a time when the option input is open circuit - either during switch transition, or during any switch bounce

With the pull-down version, there's no open circuit possibility (could still get bounce though, so maybe a capacitor as well would be a belt and braces approach)

[steve100]

How would you wire in the switch debounce capacitor - could it be fitted easily in the Vref / TPS Option circuit board area ?
Thanks
Steve

[steve100]

Even simpler way to do this is to fit a 1k resistor in place of L1 as before.
Then on the wiring away from the MJ plug, just connect the VRef line and the Option lines together and wire these both to the Map switching switch ( switch to chassis earth for Map1 and switch open for Map 2)
Hey presto, no mods to the board at all!
It works very well.
Regards
Steve

[lotustwincam]

I have read the above and understand that it refers to a unit with a MAP sensor.

For TPS, can I simplify the wiring for the option switch by connecting a 1k pull-up resistor between molex connector pins 4 and 7?

Or is connecting the resistor to the non-regulated vehicle supply asking for trouble?


Thanks

Drew

[MartinM]

For a TPS unit, just to what it shows on:
http://www.autosportlabs.net/MJLJ_V3_ve ... tion_guide

....no resistor required at all!

[lotustwincam]

Yes, I understand that.

However in an effort to simplify the wiring, by using a pull-up resistor I was hoping to utilise an unused SPST switch that is already fitted to the vehicle, with just a single wire running to it

[brentp]

Yes, if you have a SPST switch you can also use a pull-up resistor between the VREF output and the option input.

Your SPST switch, then, would switch ground. So you could potentially have only one wire going to your switch.

The cleanest way might be to wire it internally on the MJLJ PC board.

Regards,

[DannyP]

Since my MJLJ will be behind the passenger seat, my switch will be right on the MJLJ case

[lotustwincam]

Quote (... if you have a SPST switch you can also use a pull-up resistor between the VREF output and the option input. )

I considered this but if I take it from the VREF line, surely that will be placing a 1k shunt across the TPS pot when the switch is closed?

Hence my thoughts of a 1k resistor directly between pins 4 and 7 of the molex connector. Plenty of room on the reverse side of the board!