Questions on ultrasonic distance finder

[Acetronics2]

Hi, Kamikaze,

What a Bins to download the files from that site !!! ...

and , in the end ... you get a code to download the " LCD + Keyboard " project ...

Someting to correct, I wonder ...

Alain

[Kamikaze47]

Not sure about that. I didn't use any of the code from that site - i wrote my own in PBP.

All i used from that site was the receiver amplification/detection part of the circuit shown there.

[lilimike]

Hi Kamikaze,

I guess the answers to my questions is test and evaluate, in this case I am on the right track.

I started to design arround This guy's project but I was never able to observe what I was expecting on the scope for the input amplification stages and I was not completely understanding what I was doing so I've decided to start with the basics and found this link from Les Johnson which is really basic and I am having some difficulties understanding 100% of his code but I do get the basics.

I am pretty close to a newbe with PBP Pro and PICs, but I am really good at playing sounds on piezzo and blinking LEDs and I think now I am good with LCDs so like I said, I have a long way to go.

I was wondering if it is better to do more hardware and less code or vice versa but I guess the opposite is better since it is faster to change code than it is to change hardware, I am just not sure yet where I have to draw the line.

I am presently intensivelly playing with timers and interupts and I must say I am having a lot of fun trying to understand but as I am doing this on an average of 16 hours per day, I should get the hang of it in no time.

While I am at it maybe if someone can explain something; in my code I have

CMCON = 7                   ' Disable comparator
INTCON = $80                ' Disable interupts
T1CON = 0                   ' Timer1 off, prescaler 1:1

and then I do this:

    
TMR1H = 0:TMR1L = 0
T1CON.0 = 1
PAUSEUS 1
LCDOUT $FE,$80,"TMR1H = ", dec TMR1H
LCDOUT $FE,$C0,"TMR1L = ", dec TMR1L

I get: TMR1H = 4 and TMR1L = 23

What I understand from the datasheet is TMR1H cycles when TMR1L overflows so the value I am getting is actually:
4 x 65535 +23 ?

how did it get do far with PAUSEUS 1 ?

Then if I do PAUSEUS 2
I get: TMR1H = 4 and TMR1L = 24

I am confused!

Mike

[Kamikaze47]

TMR1H increments when TMR1L overflows at 256. So its 4x256+23.

Keep in mind that the timer will run at 1/4 the frequency of your main oscillator.

edit: also, pauseus 1 will not result in a 1us pause because pauseus has a minimum pause time. have a look at pauseus in the PBP manual.

[Ioannis]

Do you really have to built it yourself?

Look at the http://www.robot-electronics.co.uk/a...c_Rangers.html

Once I had to built that ranger in 1990 but then I could not find ready made modules.

After a few year I tested the modules of the above link and was surprised.

First of the idea to drive the Tx US transducer by the well known MAX232 chip (it can produce fast +/- 10 volts of pulses!) and second by its simplicity and performance.

Ioannis

[lilimike]

Well the main reason why I want to build it myself is to learn everything about it, I really like the challenge and when I go to bed just about every other day or so I sleep well because I like the feeling of having learned something new.

Now trying to calculate and figure how I got this result on my display is probably going to keep me up for a few days because even after Kamikaze's response I am still confused. Maybe it's all about the timing differences between the speed my brain works and the speed of a PIC at 4MHz.

Or maybe I am trying to calculate something that is uncalculatable!

[Kamikaze47]

OK, if you are running your PIC at 4MHz, then the timer will run at 1MHz, which means that TMR1L will increment every 1uS (when the prescale is set to 1:1).

timing the command PAUSEUS 1 will not give you a result of 1 becuase of 2 reasons. First, PAUSEUS has a minimum pause time and 1uS is so fast that the time it takes to check the timer value comes into play.

Try this:

temp VAR word

TMR1H=0 ' Reset timer value
TMR1L=0
T1CON.0=1 ' Start the timer
PAUSEUS 1000 ' Pause 1000uS
T1CON.0=0 ' Stop the timer
temp.HighByte=TMR1H
temp.LowByte=TMR1L
LCDOUT $FE,$80,"TMR1 = ", dec temp

The LCD should display somewhere around 1000 - Probably a little more because of the time it takes to start and stop the timer.