Train Tachometer Interface box help!

Thread Starter

João Paulo

Joined Jul 14, 2015
2
Hard Summer Project!!

What have I got into? Hahaha :D Basically I have to build instrumentation to sense position and signal of a train tachometer sensor and display position and speed on LCD. The problem is I have almost none background on eletronics but I am willing to learn the maximum I can and I hope you could help!

Here are the specifications:

Below please find the spec of the tachometer interface box,

speed calculation position calculation relative & abs
seven segment LED to display position (comedy size)
position display on LCD
serial interface in/out to PC using FTDI lead
isolated zero volt output for channel A/B (operate up to 30 V, check)
three LEDS to indicate speed units (m/s, km/h, mph)
push button to reset relative distance
input/output immune up to maximum rating 60V
supply for the tachometer 12V (check)
switch for the supply
ERROR detection for QA/QB
Maximum speed of train 50 km/h

For the project I have to choose the PIC, which I am left into darkness. And also I have to read some backgrounds in quadrature encoders, signal conditioning, pic programming(change notification interrupt and input capture module, etc).

I really wanna learn about it and also make a good project( and impression) and that's why I'm gathering as much help as I can!

Any questions please ask!
 

crutschow

Joined Mar 14, 2008
34,420
What is the nature of the tachometer signal you are trying to monitor?
You need to display both speed and position from this one signal?
What does "isolated zero volt output for channel A/B (operate up to 30 V, check)" mean?
Need more info to help you.
 

Thread Starter

João Paulo

Joined Jul 14, 2015
2
What is the nature of the tachometer signal you are trying to monitor?
Digital

You need to display both speed and position from this one signal?
Yeah, actually there are two channels one is shifted by 90 degrees from other, they serve to inform if the rotation is clockwise or counterclockwise, but I'm going to use only one of them, once I just need the absolute position.

What does "isolated zero volt output for channel A/B (operate up to 30 V, check)" mean?
From what I undestood I need to isolate the signal for safe work with the pic, I have to use a optoisolator in order to do that.
 

MaxHeadRoom

Joined Jul 18, 2013
28,684
If you want to do this with a pic, and certainly they have the capability, it is quite a comprehensive starter project for a newbee, particularly with no electronic experience.
The PIC has a function known as CCP Capture/Compare/PWM, some have several of these, the Capture can be used to to detect not only rpm but direction from the 90° quadrature pulses, you would not require high resolution for this.
The timer used by the Capture input can use a 38Khz clock crystal to aid in the accurate timing.
You would also have to decide on the programming language C or Assembly, you also would need a Pic programmer of some kind.
Why is isolation required, especially on a vehicle?.
If you have all summer you may make it!;)
Max.
 
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