Older Smiths Tachs etc not working Solution Found :-)

Josh_b · Post by **Josh_b** » Sun Jun 12, 2005 5:48 pm

i sorted it, i made a little circuit up and just tested it, i tried a smiths tach and a vdo tach and they both work fine! if anyone is interested i will sort out a circuit diagram, it basicly converts the MjLj RPM output into a signal older tachs can use

mini1071s · Post by **mini1071s** » Sun Jun 12, 2005 8:00 pm

Well done for sorting that out! Could I have a copy of the circuit please? Thanks.

mini1071s@hotmail.com

Josh_b · Post by **Josh_b** » Sun Jun 12, 2005 10:14 pm

hehe, i put the diagram in the files section, I just added a much simpler version also thatstill seems to drive smiths type tachs from the MJLJ output

mini1071s · Post by **mini1071s** » Mon Jun 13, 2005 11:11 pm

Thanks!

steve_c · Post by **steve_c** » Wed Jul 01, 2009 10:14 am

I'm interested in this., but can't find the files section!! can someone direct me?

dave9469 · Post by **dave9469** » Fri Jul 03, 2009 1:08 pm

Steve

I think this is the diagram Josh made but I don't know if there have been any updates to it, it says it's version 2.

If you use it let me know because I'm intending using a smiths gauge from a scimitar.

Dave

Post by **brentp** » Fri Jul 03, 2009 6:17 pm

It's important to note- this circuit was designed to accommodate the MJLJ V2/V3 design; In MJLJ V4 the TACH_OUT circuit was changed to essentially the same circuit as Dave posted.

Gilesy998 · Post by **Gilesy998** » Fri Jul 03, 2009 10:57 pm

Is this meant for the RVC voltage-sensing type tachos? ie where the original coil -ve would simply have been connected to the tacho's singal input, rather than the older loop-through style RVI inductive sensing type?

steve_c · Post by **steve_c** » Fri Jul 10, 2009 9:12 am

At a guess I would say this was for the RVC type tacho's. Mine's an RVI. The current handling capacity of the BC108 is only 100mA so I would guess that this would burn out if connected to the RVI. I don't know the impedance of the RVI tacho so can't say for certain. I will do some checking over the weekend. I don't particularly want to spend out for another tacho if I can get away with a simple high current switch.

Josh_b mentioned in one of his posts that another member (lotus68racer?) had "run the 12V common lead to the coils from the tach", thereby running the coils primary current through the tacho in a similar manner to how the RVI tacho would have worked in a distributor system. Does anyone have any further info on this mod?

Autosport Labs