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GTBecker
Joined: 18 Jan 2006
Posts: 457
Location: Cape Coral
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Posted: 07 December 2009, 0:17 AM Post subject: Centech IR Thermometer |
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FYI, an inexpensive ($4 on sale at Harbor Freight) IR thermometer yields useful data by hacking a pair of points on its circuit board. TTL data and clock are clearly labeled; the clock runs at ~2.2kHz, which even an original ZX-24 can keep up with to bit-bang-shift in groups of 40 bits to five bytes. Two groups are close enough to consider 80 bits, so the code is written to expect that worst case.
I'm using this to measure the temperature of the heater in a carbon monoxide sensor ( http://www.sparkfun.com/commerce/product_info.php?products_id=9403 ), very well. The 16-bit data provides 1/16th degree C resolution above zero Kelvin. I powered the thermometer by dropping 5v from the processor through two diodes; it might run at 5v, but I haven't tried that.
| Code: | ' CenTech_IR_Thermometer.bas
' 2009-12-06 GTBecker
' reads serial data from CenTech IR pocket thermometer, needs ~3-4v power
' ~2.2kHz negative pulse clock, data read on falling (leading) edge
' data is in groups of 40 bits (five bytes), MSB first, at ~3Hz
' temperature data is in 16th degree Kelvin
' Typical data:
' DataType?, TempHiByte, TempLoByte, Checksum, Terminator
' 76 22 201 43 13 = Target Temp 91.41C
' 102 18 218 82 13 = Ambient Temp 28.48C
' 83 0 0 83 13 = Unknown
' Typical program output:
' 84.98C 76 22 98 196 13
' 85.29C 76 22 103 201 13
' 85.66C 76 22 109 207 13 83 0 0 83 13
' 85.91C 76 22 113 211 13
' 86.23C 76 22 118 216 13
' 86.48C 76 22 122 220 13 83 0 0 83 13
const pinClock as byte = 19
const pinData as byte = 18
dim DataIn(1 to 10) as byte
Sub Main()
dim t as long, ByteCount as byte, j as byte
call Sleep(1.0)
call putpin(pinData, zxInputTriState)
call putpin(pinClock, zxInputTriState)
do
t = register.rtctick
do
if not cbool(getpin(pinClock)) then
t = register.rtctick
end if
loop until (register.rtctick - t) > 25 ' wait for >~50mS no clock between bursts
for ByteCount = 1 to 10 ' for up to ten bytes (two groups are sometimes immediately adjacent)
for j = 1 to 8 ' get eight bits
do until not cbool(getpin(pinClock)) ' wait for clock low
loop
DataIn(ByteCount) = DataIn(ByteCount) * 2 + getpin(pinData) ' shift next bit in
do until cbool(getpin(pinClock)) ' wait for clock high
loop
next
t = register.rtctick
do until not cbool(getpin(pinClock)) ' wait for clock low
if (register.rtctick - t) > 2 then ' end of group if > 2mS elapses before next clock
exit for
end if
loop
next
dim TempOut as single
TempOut = csng(makeword(DataIn(3), DataIn(2))) / 16.0 - 273.15 ' temp data is 1/16ths degree Kelvin
Console.Write(fmt(TempOut, 2) & "C ")
for j = 1 to ByteCount ' show raw data
Console.Write(" " & cstr(DataIn(j)))
if 0 = (j mod 5) then
Console.Write(" ")
end if
next
Console.Write(chr(13) & chr(10))
loop
end sub |
Last edited by GTBecker on 07 December 2009, 20:36 PM; edited 1 time in total |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 07 December 2009, 0:52 AM Post subject: Re: Centech IR Thermometer |
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| GTBecker wrote: | | FYI, an inexpensive ($4 on sale at Harbor Freight) IR thermometer yields useful data by hacking a pair of points on its circuit board. |
Nice find.
| GTBecker wrote: | | [...]which even an original ZX-24 can keep up with |
That looks like a Beta ZX-24 (square pins instead of round, 100 ohm resistor instead of an inductor near pin 12, patch wire on pin 6). |
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mikep
Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX
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Posted: 07 December 2009, 1:16 AM Post subject: |
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I still have my Beta ZX-24 as well as all of my own devices: ZX-24e, ZX-24ae, ZX-128e, ZX-1281e, ZX-24pe, ZX-24ne, ZX-128ne, ZX-1281ne, ZX-328nu, ZX-24pu, ZX-24nu  |
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