Digital Speedometer

fenderman

As the title suggests, I am building a digital speedometer to go in my car to work alongside the stock speedometer. The stock speedometer is electronically driven with pulses sent from the car's computer. I plan to tie into this wire (the VSS wire) to acquire the speed data.

I think I have the programming part basically worked out, but I want to know what the best way is to power the Stamp from the car's electrical system since they are notorious for being noisy. I know voltage regulators are popular but wondered if there was a more efficient way to power the circuit (the links I've come across around here are dead). I'd really like to use a separate power supply if I could, but if I understand circuits correctly this would cause the VSS signal to be unreadable.

Any help would be appreciated. Thanks!

-Jeremy

stamptrol

Hi Jeremy,

I've done many Stamp installations on mobile equipment and powering the Stamp is not that tricky.
For low current projects (less than 0.5 amp), a standard 7805 regulator, properly mounted and using the recommended capacitors will work fine.
For higher current, go with a switching regulator like the PT5101N or it's brothers. Again, use the recommended capacitors on the input and output.
Be sure to show us pictures of the finished project!
Cheers,

fenderman

Thanks, Tom.

PJAllen

I am not sure what is being contemplated here. A BasicStamp has its own 5V regulator on-board. If you're doing O-E-M, it's another matter.
The BoE has a 3-terminal regulator, but that 5V (V_dd) is for the externals, it doesn't run the BS2.

PE - It's unusual that a signal lead would be labelled "VSS", but not unimaginable, nothing much would surprise me anymore. Around here V_ss is what "we" call Ground (GND, Common.)

fenderman

VSS = Vehicle Speed Sensor. It's labeled VSS in my car's wiring diagram. Don't worry- I am aware of the differences between the two and will be sure not to get them mixed up.

EDIT: I just got a BoE recently. The other programmed parts I've dealt with are a simple IC that is either programmed once installed into the circuit or programmed in a programmer connected to the computer and then installed on the board. I've never seen a programmed part come already installed on a board (with the exception of the BoE which I just took to be something that was set up for easy learning), so please forgive my ignorance.

Spiral_72

The BOE isn't really the programmer either..... The Microcontroller is programmed right on the IC via serial..... Pretty slick eh?

The BOE is more of a prototyping platform where everything is available for convenience. You can actually remove the micro and power it all by itself if you want.... either 5V or 6-12V on two separate pins.

it sounds like a cool project. what kind of display are you using ??

fenderman

Sorry for the long absence-
I am using a set of 3 seven segment displays. However, unlike most seven segment displays these are vintage units that use bulbs instead of an evenly lit segment so you get a cool looking glow that is bright in the center and then fades at the edges. I am going to replace the incandescent bulbs with LEDs so that I can drive each segment directly from each output pin and then I am going to multiplex the digits for both current and real estate conservation.
Thank you for the input- we've had some other priority things pop up so I haven't had time to play with the STAMP recently but I will try to keep you all updated as things progress.