Electrical guru's inside (semi-automotive relay help needed)

[dville_gt]

Would have posted this in the garage, but this isn't so much an automotive question as it is an electrical one.

What I need:
I basically need some type of latching relay (or set of relays) that will allow me to complete a circuit via a switch (ideally a toggle, but possibly momentary), then break the circuit upon the RELEASE of a different momentary switch.

Problem: Bought a new 2-step from MSD, one "feature" incorporated into this unit is that it won't activate the 2-step limiter unless the RPM's are 1/3rd lower then the set point.

I.E. 4000 RPM set point requires the engine RPM's be lower then 2700rpm when it is activated.

This is a problem for any turbo car that is going to attempt to build boost as it stages since RPM's will most definitely be higher then the acceptable activation RPM as the car approach's the beams.

I use the transbrake button to activate the 2step so as I get staged (with the rpm's up via footbraking it), I can then hit the t-brake (and thus the 2step), hammer the gas and wait for the lights to drop.


Seems like what I need is some type of latching relay that activates upon the RELEASE of the momentary switch. Then I could bump the transbrake button as I approach the beams (thus activating the 2 step upon the RELEASE of the T-brake), then prestage/stage/grab t-brake, and as soon as I let go of the t-brake have it deactivate the 2 step.

[BERNIE MOSFET]

A relay based JK latch might work.

[juiceweezl]

Garage forum what?

[TexasT]

Add another switch or nc relay to the circuit. If the switch is closed and/or the relay is closed the circuit operates unit you release/flip switch and/or hit the relay opening the circuit.

[dville_gt]

Could I not put constant voltage to a latch relay, then use the t-brake to switch to actually break the circuit. That way when I release the t-brake button the first time (at idle, thus fulfilling the requirement needed to activate the 2-step) it activates since it gets energized at that point, then when I press the t-brake button again once staged it breaks the circuit again and once I release it it energizes the latching relay again thus breaking the connection.

In this configuration the latching relay would normally have voltage applied to it and the button would actually break (not make) the circuit, and releasing the button would "re" energize the relay thus switching it either on or off depending on what state it currently is in.

Only problem would be if the latching relay could handle having voltage applied to it for long periods of time vs. short spurts that it would normally expect.

[Tyrone Biggums]

Try a Standard part number AR585.

[dville_gt]

not seeing anything with that part number.

is there not some configuration of bosch relays i could use to break a circuit upon release of a momentary switch?

[BERNIE MOSFET]

If I understand correctly, the behavior you want:

As you approach the beams, you want to on/off the tbrake to activate the MSD. Then, engage tbrake and when it releases, MSD is turned off.



if so, this could work if you want to use relays(it is ugly):

http://tams-www.informatik.uni-hamburg.de/applets/hades/webdemos/05-switched/20-relays/flipflop4.html

Use a on/off toggle switch in series with a secondary normally closed relay for the tbrake (if the tbrake is not normally closed) and an indicator that MSD is on. Press/release momentary and MSD toggles on. Second press/release toggles MSD off. If you have a normally open momentary(tbrake), then the toggle action will occur on the depression of the switch, and not the release.

But, I'm thinking three 4PDT relays is not the way to do this.

You could do the same thing with three 4-switch ICs; the last output controlling a relay-toggle IC switch on/off the MSD.

Switch IC:

http://datasheets.maxim-ic.com/en/ds/DG411-DG413.pdf

Automotive toggle IC:

http://www.atmel.com/Images/doc4771.pdf

This is probably more involved than you would like. I'm not familiar with anything off the shelf that does what you want, but that doesn't mean it doesn't exist. When I get home I will see if there are less complicated ways to get the behavior you want.

[dville_gt]

How about this.

Use the brake light + to trigger the 2 step, then use the trans brake momentary (which is negative) to trip a relay that provides + to the 2 step as well. This way when I am foot braking it up to the line the 2 step is on, when I get staged I grab the t-brake (which keeps the 2 step activated when i let off the brakes). When I let go of the t-brake it deactives the 2 step and down the track I go. When I get to the big end and hammer the brakes it won't activate the 2 step since it doesn't activate until the rpm's are less then 2/3rds the set level.

Seems like it would work.

[BERNIE MOSFET]

How about this.

Use the brake light + to trigger the 2 step, then use the trans brake momentary (which is negative) to trip a relay that provides + to the 2 step as well. This way when I am foot braking it up to the line the 2 step is on, when I get staged I grab the t-brake (which keeps the 2 step activated when i let off the brakes). When I let go of the t-brake it deactives the 2 step and down the track I go. When I get to the big end and hammer the brakes it won't activate the 2 step since it doesn't activate until the rpm's are less then 2/3rds the set level.

Seems like it would work.

Engineers don't always come up with practical solutions.


That's practical.

[Mysticcobrakilla]

Engineers don't always come up with practical solutions.


That's practical.

Shit!!!


He can tune engineers now?

[dville_gt]

The only issue I'll have to figure out will be the burnout. I use a line lock but the brakes lights are on a pressure switch that is tied into a front brake line. Thus the brake lights are on during the burnout even though my foot is not on the brake at all. I obviously don't want to have the 2 step activate during the burnout. I guess I can just put in a toggle for the 2 step that I flip after the burnout, I just hate adding to the list of things to remember before making a pass.

[BERNIE MOSFET]

I knew I had seen this behavior on a flipflop! I couldn't remember how though.

If you want to keep the brake lights out of this, I think this is a better solution than the one I had before:

Use a single Dtype flip flop IC, instead of the 3 switch ICs. The tbrake connects to the clock, and the Qbar output connects to the Dpin input. The flip flop output (Q) can control a power transistor if the MSD draws any appreciable current, making a relay unnecessary. Wire everything to a protoboard and install to a small box. It could be a simple $20-30 home-brew module that you could plug a parallel tbrake line into and output to MSD.

http://www.onsemi.com/pub_link/Collateral/MC14013B-D.PDF