ds18b20: negatives handled
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278e3541d3
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@ -5,10 +5,11 @@
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-- Vladimir Dronnikov <dronnikov@gmail.com>
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--
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-- Example:
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-- for k, v in pairs(require("ds18b20").read(4)) do print(k, v) end
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-- require("ds18b20").read(4, function(r) for k, v in pairs(r) do print(k, v) end end)
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------------------------------------------------------------------------------
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local M
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do
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local bit = bit
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local format_addr = function(a)
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return ("%02x-%02x%02x%02x%02x%02x%02x"):format(
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a:byte(1),
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@ -16,7 +17,7 @@ do
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a:byte(4), a:byte(3), a:byte(2)
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)
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end
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local read = function(pin, delay)
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local read = function(pin, cb, delay)
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local ow = require("ow")
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-- get list of relevant devices
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local d = { }
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@ -37,25 +38,32 @@ do
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ow.skip(pin)
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ow.write(pin, 0x44, 1)
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-- wait a bit
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tmr.delay(delay or 100000)
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tmr.alarm(0, delay or 100, 0, function()
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-- iterate over devices
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local r = { }
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for i = 1, #d do
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tmr.wdclr()
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-- read rom command
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ow.reset(pin)
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ow.select(pin, d[i])
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ow.write(pin, 0xBE, 1)
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-- read data
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local x = ow.read_bytes(pin, 9)
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if ow.crc8(x) == 0 then
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local t = (x:byte(1) + x:byte(2) * 256) * 625
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-- NB: temperature in Celcius * 10^4
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r[format_addr(d[i])] = t
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d[i] = nil
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local r = { }
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for i = 1, #d do
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tmr.wdclr()
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-- read rom command
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ow.reset(pin)
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ow.select(pin, d[i])
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ow.write(pin, 0xBE, 1)
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-- read data
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local x = ow.read_bytes(pin, 9)
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if ow.crc8(x) == 0 then
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local t = (x:byte(1) + x:byte(2) * 256)
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-- negatives?
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if bit.isset(t, 15) then t = 1 - bit.bxor(t, 0xffff) end
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-- NB: temperature in Celsius * 10^4
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t = t * 625
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-- NB: due 850000 means bad pullup. ignore
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if t ~= 850000 then
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r[format_addr(d[i])] = t
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end
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d[i] = nil
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end
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end
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end
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return r
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cb(r)
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end)
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end
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-- expose
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M = {
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