TPMS... DIY and Design Anatomy

[srt8-in-largo]

Thanks guys!

The hardest part of the install will be pulling the shelter cover to get to the underside of the Honda plaque and routing the alert LED. I'm hoping to develop the low frequency (LF) communication so that riders can get a fresh reading just by turning the key to ACC. These LF communication modules will need to be mounted near the tires... and I haven't yet worked out how all that will come together.

I plan to use an in-tire sensor that will mount to the rim on the opposite side of the air valve. This creates a better tire balance and, more importantly, allows you to use tire sealer like Rideon and not worry about that stuff clogging the sensor. Like this picture from the Mobiletron manual.

[Phantom]

[srt8-in-largo]

Thanks Phantom!

I built a test chamber with a pressure gauge, thermocouple, and a schrader valve to let me test out the sensor board. PVC in general is NOT a good material to pressurize, especially the type that says "not for pressure", but it did ok to 40 psi. The sensors seem to be working fine.

The part of the system that I've been concerned with was the antenna circuitry; currently it has no filtering and a first pass design of the matching network. To test how good (or bad) it is I downloaded HDSDR and bought a $20 antenna to go with it. The video below shows the sensor transmitting at a distance of about 4ft from the antenna. From what I can see, I think Freescale designed a helluva RF transmitter on the chip! Even with this non-optimized proto-board signal strength is fantastic.

For test purposes I have the transmitter configured to send 16 consecutive packets... these are the pulses and beeps you see. Each packet contains pressure and temperature data measured by the chip. I plan to have the software setup where it'll take measurements every 0.5 or 1 second but only send the packets every 20 or 30 seconds in order to conserve battery power. I might even extend the transmission to 60 seconds or more... but I have yet to create a power budget. Like I said above, I want a sensor with long battery life.

Sending consecutive packets is done for redundancy; if one packet gets lost there are multiple others available and therefore the data monitoring can be consistent and continuous. When I look at the power budget and do some link testing I'll probably reduce the number of packets to 2 or 4 to, again, optimize battery life.

In addition to the above software configuration, I plan to create a comparison loop where if a significant pressure drop is detected the chip will transmit immediately and more frequently.

I've also been working on the receiver module. Next steps are to get the transmit-receive link operational and then work on incorporating the LCD display. Here's a picture from the vendor website; I think this is with the white backlight turned on.

[hiflyer]

Thanks Phantom!

I've also been working ......

srt8, I think that's an understatement!!! You are serious about this thing!! Get er done!!

[srt8-in-largo]

Haha thanks Flyer; I hope I can get it all together before long.

To illustrate the transmission options, I reduced the packet count to 4 in this video and maxed out the time between each of the four packets. I have the program compiler in debug mode and you can hear me clicking the keyboard to initiate each transmission; when the chip is programmed it'll do this automatically.

[Fla_rider]

This looks great! I'm sure you will have many board members wanting this! I'm pretty lazy so having this tell me the tire pressures is the cat in pajamas!

[srt8-in-largo]

Thanks John. I didn't start this project with the intent of selling them but if people like it...