USB powered Pressure transducer

Hey everyone. Im going to be attempting to make a usb powered pressure transducer for in cylinder testing. I ordered 3 300 psi transducers from ebay for 66 dollars. Now i just have to get some quick connect fittings and then rig a usb plug and a probe to the wiring. Ill keep you guys posted on how it goes. If it ends up being successful im going to make 4 of them so i can do a cranking compression test on 1 bank of cylinders at a time and speed the process up.



I plan on using a usb hub that you can plug in. Being that usb uses 5v thats perfect for this application. Ill do some voltage tests on the hub also and see how close to 5v we get. Right now i have to figure out how to attach the transducer to the quick connect fitting because the threads are not the same but im sure theres a thread adapter i can buy. Ill keep everyone posted on how it goes

Update: im just going to use 1/4 npt female quick connector and going to buy some 1/8 to 1/4 " npt thread adapters from fastenal tomorrow

The tranducers are not actually that sensitive to over supply voltage and can cope with around 7 volts input but I found the best solution was to use a BEC (somtimes called UBEC) which is a tiny low cost low noise device which will step any voltage from about 28.8 volts max down to a very stable noise free 5.00v. BEC/UBEC is a type of Buck convertor are used by drone builders and are available very cheaply via eBay or online drone and radio control shops. You can run a BEC/UBEC off the vehicle battery or from a 9v PP3 (MN1604) battery. They are usually rated at 3 amps max.
I would suggest you really don't need 4 transducers keep it simple , just use a either a curent or voltage cranking compression test first to identify any suspect cylinders.
The major weak spot with a hombuild setup is the flexible hose from the cylinder to the tranducer normal compression test hoses are not designed to take the repeated pressure reversal experienced during a running compression test and the inner liner of the hose tends to collapse

Thanks for the info!

Four transducers? :woohoo: Probably a bit overkill, but man it sounds awesome! I'm imagining having four running compression waveforms in a parade on the screen :ohmy:

Definitely keep us updated!

Yup thats the idea. Im going to start a mobile doagnostic/repair business and want to be as efficient as possible.

Or I could use 1 to check compression, 1 to check fuel pressure and use the third as a backup if one fails

Great man, really like to see where this goes! :woohoo:

So far I have the sensors attached to a 1/4" npt air coupler. Had to buy a 1/8 npt female to 1/4 npt male. Now I just need to source some long usb cables with two power wires, some heartshrink transition boots, and some sacrificial test leads. I'm going to use banana plug leads and use bnc/banana adapters.

I would be cautious about using USB power for sensors without filtering. The 5V on the USB bus is not regulated that well on many PCs and in addition many PCs will not actually provide 500ma out of each port. On a laptop you might have a total limit for all USB ports, so the more USB devices the less power per device. The USB bus is also VERY susceptible to electrical interference, you could couple enough engine noise onto the sensor power leads to cause the PC problems.

An alternative might be a rechargeable battery pack. Years ago I set up one for a friend to power a couple laboratory grade accelerometers/temp sensors (for bearing life measurement). It was designed for charging laptops but it also had a 5V output. These days there are loads of cell phone charger battery packs out there, look for a good quality unit that can supply the amount of current you need.

Thats not a bad idea! I was thinking about using a pluggable hub that has at least 2A so that way theoretically you get 500ma on each device but a rechargeable pack would be clean and better for a mobile application. Going to check it out. If they are pretty cheap i might even do one per sensor

Did you get this finished ? How do they work? What do you use for hoses ? I've heard that standard hoses don't hold up to running engine in cylinder captures I've been thinking of using hydraulic hoses.

Sent from my SM-N920P using Tapatalk

hi, i was going to finish it and then got sidetracked with work and I'm in the process of starting my own legit mobile repair shop. been acquiring shop equipment and doing legal paperwork so been swamped. ill be doing it soon though