Introduction: Pulse Sensor for Automotive Diagnostics (27mm Piezo)

This is a homemade version of the "First Look" sensor. Youtuber - Forklift Geek inspired many to create their own version of it. His design used plumbing fittings as a housing. Even though, being a previously licensed plumber, I wanted a little more appealing looking sensor (truth: I couldn't find the right size piezo to fit) :> I had some 27mm piezos and I just decided to print my own housing. Here it goes.

Required items/tools:

1st and most importantly: 3D printing capability

2nd: 27mm piezo (they are all over eBay)

3rd: Female BNC connector chassis type (everywhere too)

4th: Soldering skills and equipment

5th: Small pliers

6th: Well maybe this is the most important item, an oscilloscope. But then again would you be here if you didn't have one?

Step 1: Printing and Afterwards

The files can be found at this link:

Thingiverse Thing #4351397

1st: Check solder connections on the piezo..cause you get what you pay for..

2nd: If possible check polarity of the piezo. The black wire (outer ring) connects to the center pin of the BNC in my instance but I'm not sure if that is across the board. I recommend cutting the wires so that they are about 1-1/2" long. This keeps them from interfering with the piezo movement.

3rd: Be sure to either tighten down the BNC before soldering OR make sure that you have the correct layout as shown above so that you don't end up needing to unsolder your center connection.

4th: Complete your connections and tighten the BNC nut.

Step 2: You Should Be at This Point

Hopefully everything went right the first time. You should have something similar to the photo. If you didn't shorten your piezo leads, You may want to rotate the piezo and BNC opposite of each other so that the wires start to curl and pull taunt. If any of the excess wire presses against the piezo it may effect your readings.

Step 3: Assemble the Body and the Cap

As you see in the photo, you'll need to glue the cap inside of the body. Just run a small seam of glue around the cap and slide the cap in. The piezo will fall into place and the cap and body should be flush.

Step 4: Basically Done

You can see that the top of the cap lines up with the edge of the body. Once dried, you have a finished product.

Step 5: Fitting the Barbs

The barbs are 1/4" mip and come in 1/4", 5/16" and 3/8" hose sizes. Since this will accept 1/4" mip, you can also utilize a brass barb. At first it may not seem that the barbs thread into the housing but they will, they just need a little convincing. If you run them in a little, then back out, tap style, they get to the point where they go in by hand. I don't put anything on the threads nor do I recommend it. Again, we are not going for a perfect seal.

Step 6: Testing & Summary

Here is the signal of the sensor shown in the photos. It works real well and it probably only costed a dollar (yea, yea I know you had to buy a whole pack of piezos and a whole pack of BNC's but still....). It is recommended to hang the sensor from the hood using a bungee. This is to reduce hard vibrations that can alter readings.

I hope you like my Instructable! I think that this is a must have tool for advanced vehicle diagnostics. I wish every one luck in building and utilizing this. Just a reminder, this is not to be produced and sold for financial gain! If you'd like a ready built pulse sensor (his design, not mine), please see Cody's Auto Diagnostics. If you're looking at this Instructable then you probably already know about (youtubers):

South Main Auto

Pine Hollow Auto Diagnostics

KY Home Garage


Super Mario Auto Diagnostics

Advanced Level Diagnostics

Schrodinger's Box (QM)

Logical Canuck

and let's not forget the king... New Level Auto

If not then please subscribe to them. The knowledge that they freely give is awesome.

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