Options switch resistor...

Edwardatherton · Post by **Edwardatherton** » Tue Aug 07, 2007 9:42 am

I am fine with electronics when there are two wires - if they spark they are the wrong way round! However, as I have found out, the PCB doesn't like sparks and such-like so I am trying to avoid doing that again...

Could someone please tell me exactly what part number (from Maplin would be handy) I need to buy for the dual mapping switch?

Can it be wrapped in heat-shrink tubing to avoid any shorts, or what is the recommended method if not?

Thankyou for any help!

MartinM · Post by **MartinM** » Tue Aug 07, 2007 4:58 pm

If you are wiring up the switch as in http://www.autosportlabs.net/MJLJ_V3_ve ... tion_guide then you need a SPDT (single pole double throw) switch

If you want small then Maplin part FH98G, if you want big then Maplin part JK27E

Edwardatherton · Post by **Edwardatherton** » Wed Aug 08, 2007 8:04 am

Thanks MartinM, I already have the larger of those switches.

It was the way I worded it but what I meant (without actually managing to say it!) was the resistor - what part number for the resistor...

Maplins have various different types and wattages of resistor and I don't know the differences!

MartinM · Post by **MartinM** » Wed Aug 08, 2007 8:24 am

Maplin part M1K will be fine.

Solder one end to the switch contact, solder the flying lead from +12v to the other and cover the switch contact, resistor and the soldered connection from the flying lead with heatshrink...

Edwardatherton · Post by **Edwardatherton** » Wed Aug 08, 2007 8:40 am

Thanks. Hopefully thats all the building questions out of the way!

I am getting excited now - got the vacuum tubing last night and wrapped all the wiring - just need to feed it all round the engine and through the bulkhead somewhere! There is a small light at the end of the tunnel...

MartinM · Post by **MartinM** » Wed Aug 08, 2007 10:57 am

Let's hope it's not the light from a far-away very large train heading straight towards you...I'm sure it won't be though

It's recommended to put a "U-shape" in the pipe below the level of the MJLJ has a vapour/liquid catcher - sounds a good idea but quite what happens if you actually get some liquid in the "U" I'm not sure....

If you have a MAP MJLJ then the alternative to putting the resistor physically on the switch, and to simplify the wiring, is to:
- put it on the circuit board in the position that L1 normally fits in
- connect Molex pins 4 and 6 together in your wiring harness
- use a SPST switch to earth/not earth the join of pins 4 and 6

Edwardatherton · Post by **Edwardatherton** » Wed Aug 08, 2007 11:14 am

Yes it is MAP setup.

From looking at the assembly instruction pictures, is L1 on the TPS part of the board nearest the molex connector just beside the Zener? (Looks like the L got drilled through!)

use a SPST switch to earth/not earth the join of pins 4 and 6

So I could use any on/off switch, and this would go to earth when 'on' - for example ON(earth) - OFF(nowhere!).

Just trying to work this out in my head now! When the switch goes to earth, does this stop the resistor from doing anything therefore the controller sees no voltage and switches maps?

MartinM · Post by **MartinM** » Wed Aug 08, 2007 12:05 pm

Exactly there....yes, the "L" is drilled through

With the switch OFF, the pin 4/6 join is held at a high level (5 volts) by the resistor - so one of the maps is used

With the switch ON, the pin 4/6 join is held at a low level (0 volts) since it is directly connected to earth via the switch - so the other map is used

Time for you to get experimenting

Edwardatherton · Post by **Edwardatherton** » Fri Aug 10, 2007 10:56 am

Good, that's now wired in! Should be test running it at Astle Park show tomorrow!
As I don't have a laptop to plug in while in the vehicle, and my PC is in the attic at home, how do I load dual maps with the megajolt unplugged from the vehicle?

For testing/map changing purposes, I have a 9V battery to plug in to + & -, do I then have a wire from pins 4&6 back to the - as well via a switch?

MartinM · Post by **MartinM** » Fri Aug 10, 2007 6:17 pm

Exactly that......

Edwardatherton · Post by **Edwardatherton** » Mon Aug 13, 2007 8:59 am

For some reason I am getting 6.43 volts between the battery (9V) and either side of the resistor at L1 whether or not the wires from 4&6 are going to ground or not.

How or where do I start checking what is wrong please?

MartinM · Post by **MartinM** » Mon Aug 13, 2007 9:26 am

Sound like you are measuring between the battery +ve and the pin 4/6 join? - you should be measuring between the pin 4/6 join and battery -ve/earth ...also don't measure either side of the resistor - just the "outbound" side ie the pin 6 side.

So...you should be measuring:
+5v between pin 4/6 and battery -ve/earth with the switch open
0v between pin 4/6 and battery -ve/earth with the switch closed

Edwardatherton · Post by **Edwardatherton** » Mon Aug 13, 2007 10:17 am

Ummm, just ignore the plonker here! After realising I was connecting the wrong pins to the 9V battery the two ignition maps suddenly appeared on the screen!

I have now set two maps, so I shall see what happens on the drive home!

dr.occa · Post by **dr.occa** » Tue Nov 06, 2007 5:34 pm

sorry for exhuming an old thread.

what is the recommended wattage on the 1k resistor for the option switching? i.e. 1/4w, 1/2w...etc

or is it neglible and 1/4W should be just fine?

Post by **brentp** » Tue Nov 06, 2007 8:08 pm

Yep, 1/4 is fine.