Readadc10

[alhoop]

I am using the following code to get a variable delay up to 60 seconds to control a sound board
in model railroad applications. As i know nothing about Readadc10 is the following code efficient.
In max delay I get 63.1 to 63.8 seconds which is accurate enough for my application - seems like
the +/- 1 bit showing up. I go from 08M2 vcc(4.5 volts) through a 3.9k resistor and a 5 kohm pot
to ground with the pot wiper connected to ADC input pin C.1.
I found that any voltage above 2.56 volts gave random readings. Is this normal?
Ps. I found the answer, my step of 100 was going to 102300, way over the limit of 65000+.
thanks
Al

;Picaxe 08M2 program for Sound board adapter

start:                            
pause 1000                 ;ensure that train detection is captured.
if pinc.3 <> 0  then      ;lcheck to see if controller has detected
                                     ;a train. if so   
high c.2                       ;pass +12 Vdc to sound board to activate
readadc10 C.1,w1
w1 = w1 * 100
debug w1                    ; wait for crossing gates to come down 
pause w1
endif 
                   
cont:                           
low c.2                         ;deactivate sound board
if pinc.3 = 1 then cont ;keep sound board deactivated until
                                     ;gates go up and another train is detected
goto start                     ;go back to check for another train

 

[g6ejd]

Your potential divider will not provide more than 2.52 volts and at that voltage the Pot R will be maximum, I suspect it is the Pot causing your random readings. Suggest changing 3.9 to 3.3K if you want a more reliable sweep between 0 and 2.5volts.

 

[hippy]

With the pot connected to 4.5V you can probably drop the 3.9K resistor completely and put the pot across the 4.5V and 0V rail.

That will then return a READADC10 value of 0 to 1023. To get that to 60s (60,000ms) each step would be 58.65ms. A value of 59 would therefore be a good choice as that will not overflow the 16-bit (65,535) maximum allowed ...

ReadAdc C.1, w1
w1 = w1 * 59
Pause w1

 

[eclectic]

@Al
Please see:
http://www.picaxeforum.co.uk/showthread.php?7679-Read-Me-First!

;Picaxe 08M2 program for Sound board adapter
start:                            ;line 1
pause 1000                ;ensure that train detection is captured.
if pinc.3 <> 0  then      ;lcheck to see if controller has detected
                                     ;a train. if so   
high c.2                       ;pass +12 Vdc to sound board to activate
readadc10 C.1,w1
w1 = w1 * 100
debug w1                    ; wait for crossing gates to come down 
pause w1
endif 
                   
cont:                           
low c.2                         ;deactivate sound board
if pinc.3 = 1 then cont ;keep sound board deactivated until
                                     ; gates go up and another train is detected
goto start                     ;go back to check for another train

Is easier than someone opening a text file

e

 

[alhoop]

With the pot connected to 4.5V you can probably drop the 3.9K resistor completely and put the pot across the 4.5V and 0V rail.

That will then return a READADC10 value of 0 to 1023. To get that to 60s (60,000ms) each step would be 58.65ms. A value of 59 would therefore be a good choice as that will not overflow the 16-bit (65,535) maximum allowed ...

ReadAdc C.1, w1
w1 = w1 * 59
Pause w1

Thanks Hippy:
That worked perfectly - gave a linear delay from close to zero up to 60 seconds. Where is 'step' explained and why was
the table in readadc dropped in later editions of the manual?
Al

 

[hippy]

Where is 'step' explained

It's not explained as such; it's what you would need to multiply a 0 to 1023 value by to get a 0 to 60000 result. That is -

1023 * STEP = 60000

STEP = 60000 / 1023 = 58.65

and why was the table in readadc dropped in later editions of the manual?

I am not sure which table that would be. It may have related to details of the PICAXE-08 low-resolution ADC which is fairly redundant these days as the PICAXE-08 has been superseded.