The famous (or soon to be) $30 2-step

This was recently brought to my attention in my Datsun build thread, but I'm creating this thread since this deserves its own conversation.

1. TheV8Kid is a genius.

2. TheV8Kid is awesome for sharing his genius.

3. You can make a two-step for consistent launches and building boost on the line with an old shift light and smart use of somewhat common electronics.

Watch:

I have some questions:

A. Are those Solid State Relays (SSRs) DC-DC or DC-AC? The coil signal would be a DC signal, but with a frequency equal to RPM, correct? So I would think a DC-DC is what is needed. *think*

B. What is meant by resistance = RPM? Is the RPM signal from the ECU a constant 0-5V reference (ie 1000 rpm = 1 volt, 2000 rpm = 2 volts, etc)? I thought RPM signal would be like an old school coil signal which is a frequency = RPM*4 or 6 or 8?

Excellent, excellent work. Thanks in advance.

A - It's DC to DC. He's using a signal controlled by the shift light to enable the relay (ie enable that coil).

B - Usually the RPM signal from the ECU is a square wave with the RPM relative to the frequency. The shift light is active above a certain frequency and inactive below that frequncy - it probably achieves this with a simple IC of some sort. The IC knows what frequency to use by the resistance. 

I think I found the module he used:

https://ebay.us/KCM9u7

Looks like it's up to $39 now for the 8-port one.

On your B, if I'm understanding you and him right, I think he's talking about the resistance setting the activation RPM for the shift light he used. They set the shift light activation using resistor "pills" which he swapped out for a potentiometer so he can adjust it on the fly. He then measured the "pills" and the potentiometer sweep and marked landmark spots to come up with an approximate graduated legend. Or am I misunderstanding your question?

Gotcha. Thanks for the confirmation on the DC-DC. Its what I assumed but you know what happens.

As for my second question, the square wave freq = rpm is what I expected, and it would make sense that you use an RC circuit to vary R until you match the frequency of the RPM and flip the output. So just didn't understand that language. Cool. Sounds like its possible to get that IC and make your own RC circuit instead of relying on the shift light. I still don't quite understand why another potentiometer is necessary if you're using the shift light circuitry, since the shift light should already have the potentiometer build in so that you can set the light activation point.

Unless that is what dculberson is saying, that the original shift light used resistor 'pills' that you physically had to remove from the light and replace with a different value to set the RPM activation point.

Sounds like I just solved that for myself by typing it out. Thanks guys!

Robbie (Forum Supporter) said:

Sounds like I just solved that for myself by typing it out. Thanks guys!

https://en.wikipedia.org/wiki/Rubber_duck_debugging

Looks like you could use a 'touch tone decoder' circuit in an LM567 chip to trigger the RPM at which you'd like the 2-step to come in. An LM567 should be much cheaper than a shift light! (and is probably whats in the back of the shift light to begin with).

I think this is the same exact thing that was used in the Chinese rip off of the Bee*R rev limiter. 

_ said:

I think this is the same exact thing that was used in the Chinese rip off of the Bee*R rev limiter. 

What is the beer rev limiter? 

I tried to build one of those in 2015 using the cheapest adjustable shift light i could find. In the end i was so annoyed about how they built the shift light that i figured I'd end up spending more time and money (combined, anyway) trying to cobble my way out of spending 10s of dollars and used a 'real' rpm switch.  It's possible, but it's also possible to trial and error your way past the cost of a part that's specifically designed to do the job unless you're using a proven parts list of things that will work together. 

TheV8Kid's YouTube channel is Nivlac57. Please subscribe. 
 

For those who attend the $2000 Challenge, seeing homemade items like this are relatively common. For those of you who don't attend, you should at least spectate. I have been involved in organized racing for 41 years. And I have truly learned to appreciate the hundreds of frugal solutions that folks have developed to keep costs down. 

In reply to Vigo :

That's what I'm saying! An lm567 chip should be free in any number of old telephones (I'd say shoot for one with a corded handset and actual buttons) and probably zillions of other outdated electronics. Heck even if you buy one new it's like $1.50.

And that is exactly the circuit you need. Skip the cheapo timing light altogether.

In reply to wheels777 :

I missed this awesome 2 step at the challenge and didn't see it until the YouTube was posted in another thread. I'm subscribing for sure!

The Challenge as a spectator was in my plans for this year.

I was there when Calvin came up with this and he and Andrew  spitballed it until they figured it would work. Amazing seeing what two people willing to TRY anything can accomplish.