Coming from SX to Prop need some advice.

turbo · 2011-01-25 19:36

I have been using the SX for a few years now and i have a few commercial products using them right now, my supply is getting low on the SX's and i have already started to port my code from the SX over to the Prop .

My device talks to a automotive dash through serial and that part works fine on the prop now i need it to read 2 analog signals 0-5v range , on the SX i use Analogin but i havent found a similar example on the prop , my analog signals have pullups on there lines and as they move through there range the get closer to ground.

I seen RCtime in the examples but i dont think that will work ( or will it) ?

Does PropBasic have a equivalent to ANALOGIN ?

HShanko · 2011-01-25 19:48

Look at AN001, at the sigma-delta A/D scheme. Uses two R and two C for basic design. Works for many applications.

Ttailspin · 2011-01-25 19:58

That is exactly what RC time is for, so it should work for many Analog to Digital conversions..

Have You considered the "MCP3202".? It may be something You could use.

JonnyMac · 2011-01-25 20:02

Here's a simple bit of code that let's you read an RC circuit; I use it in the EFX-TEK AP-16+

pub readpot(p)

'' Reads RC circuit on pin p
'' -- takes about 2ms
'' -- assumes 10K + 0.01uF

  ctra := (%01000 << 26) | p                                    ' ctra in pos detect mode 
  frqa := 1

  outa[p] := 1                                                  ' charge cap
  dira[p] := 1
  waitcnt((clkfreq >> 10) + cnt)                                ' ~1ms @100MHz

  phsa := 0                                                     ' clear counter
  dira[p] := 0                                                  ' allow discharge
  waitcnt((clkfreq >> 10) + cnt)
  ctra := 0                                                     ' disable ctra
  
  return (phsa >> 4) <# 500                                     ' return discharge time

Note that the last line divides the result down and limits it to 500 -- this worked for my program.

I, too, am a fan of the MCP320x family and have used it in several projects.

turbo · 2011-01-25 21:16

Thanks guys for the point in the right direction .

One last question before i dive in , will the 220ohm series resistor in the RCtime circuit be sufficient to protect the input pin from my 0-5v analog sensor since the prop is a 3.3v chip?

JonnyMac · 2011-01-25 22:05

I wouldn't use an RC circuit to measure a 5v input -- best to swtich to an ADC like the ADC0832 or MCP3202. Its okay to connect them to 5v, just put a 2.2K resistor into the DIO line. This article will help:

-- http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp8.pdf

Coming from SX to Prop need some advice.

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