Stamp Math Help

Kevin SkyMoCo

My servo's have a range of 300 to 1200, but I want to receive positions
in one byte (actually in the range 50-250). So I need to do some math
where if I receive a 50, send a position of 300, 51 move to 305, 52 move
to 310.

Since I have range of 200 inputs, a lookup table is too big, and since I cannot
use floating point, I am at a loss.

Jon Williams

This is no problem for the BASIC Stamp:

newPos = (oldPos - 50) */ $0480 + 300

You should write a little demo with the formula above to prove that it works.

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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA

Beau Schwabe

How about...

Servo = ((N*45)+3000)/10

Expanded:
Servo = N * 45
Servo = Servo + 3000
Servo = Servo / 10

or

N = (((Servo*10)-3000)/45)+50

Expanded:
N = Servo * 10
N = N -3000
N = N / 45
N = N + 50

....Where:

Servo = the Servo position (300 to 1200)
N = the byte value of (50 to 200)

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Beau Schwabe - Mask Designer III

National Semiconductor Corporation
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071

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Kevin SkyMoCo

Couple questions:

newPos = (oldPos - 50) */ $0480 + 300

What does the $ operator do? I cannot find it in the help. And, my 50-250 value
is an absolute position to move the servo to.


And when I try Beua's formula with a N of 50 I get 525, not the 300 I was hoping for..
Servo = ((N*45)+3000)/10

Maybe more example might help.
Send Stamp Move To
50 300
100 525
150 750
250 1200

Beau Schwabe

OOps...

try subtracting 50 off of N before applying the formula so that it becomes...

Servo = (((N-50)*45)+3000)/10

Expanded:
Servo = N - 50
Servo = Servo * 45
Servo = Servo + 3000
Servo = Servo / 10

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Beau Schwabe - Mask Designer III

National Semiconductor Corporation
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071

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Kevin SkyMoCo

Perfect!

My only excuse is that Calculus was 20 years ago my kids are still doing counting on
their fingers.

Tracy Allen

The $ is not an operator. It just shows that the number is written in HEX format. It could just as well be written 1152 in decimal. Inside the stamp it is the same binary number in the circuits of the stamp. The

The */ is an operator. In Jon's formula it effectively multiplies times 4.5 to achieve the scaling you need. (1152/256 = 4.5 The stamp does it internally as a multiply followed by an implicit divide by 256)


position = (serialbyte - 50) */ $0480 + 300

Here is another way...

position = serialbyte */ 1152 + 75

>Send Stamp Move To
>50 300
>100 525
>150 750
>250 1200

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Tracy Allen
www.emesystems.com