Forth-eV Wiki

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
[[en:pfw:dht22|go back]]

<code>
(* DHT22 sensor, using PIO: 480 bytes
   Willem Ouwerkerk 20250627

    40-bits pulse stream 32-bits data & 8-bits checksum

*)

chere
need arshift    \ Load ARSHIFT from library
need pio\       \ Load PIO (dis)assembler

clean-pio  decimal      \ Empty code space, start at zero
0 0 {pio                \ Use state machine-0 on PIO-0
    160000 =freq        \ On 4 * 40 kHz frequency (6.25 Ás ticks)
    05 1 =out-pins      \ GPIO 5 for OUT & SET
    05 1 =set-pins
    05 =in-pin          \ GPIO 5 for IN & JMP
    05 =jmp-pin

    0 =in-dir           \ Shift left
    32 1 =autopush

    0 pindirs set,              \ Pin is input
    wrap-target
        4 [] begin, again,      \ Wait for start command
    one ( Sensor readout )
        1 pindirs set,          \ Pin is output
        3 y set,  begin,        \ Generate start pulse low .8 ms
            31 [] 0 pins set,
        y--? until,
        6 [] 1 pins set,        \ 44 Ás start pulse high

        6 [] 0 pindirs set,     \ Now input, wait 44 Ás, skip response low
        6 [] high 0 pin wait,   \ Wait for response high 44 Ás

        31 y set,               \ Now read the 32-bits answer 6.25 Ás
        begin,                  \ This contains the sensor data
            low 0 pin wait,
            5 [] high 0 pin wait, \ Wait for high bit 37.5 Ás
            1 pins in,          \ Shift in low or high bit 6.25 Ás ( autopush
        y--? until,             \ Count all 32 bits 6.25 Ás)
        7 y set,                \ Read 8-bit checksum 6.25 Ás
        begin,
            low 0 pin wait,
            5 [] high 0 pin wait, \ Wait for high bit 37.5 Ás
            1 pins in,          \ Shift in checksum bit 6.25 Ás
        y--? until,             \ Count 8 bits 6.25 Ás
        push,                   \ Result 8-bits to fifo 6.25 Ás
    wrap
    0 =exec                     \ Start with wait loop
pio}

v: pios  also extra
: READ) ( -- data chk )
    one> 0 exec-opc             \ Start new measurement
    begin  0 rx-depth 1- until  \ Stack minimal two deep?
    0 rxf>   0 rxf> ;           \ 32-bits data & 8-bits checksum

: .DHT  ( h -- )                \ Show scaled result
    16 lshift  16 arshift       \ Extend sign bit
    s>d tuck  dabs
    <# # ch . hold #s rot sign #>
    type space ;

: CHKS  ( data -- chks )    \ Calculate checksum
    h-h  b-b +  swap        \ Split & calc. checksum
    b-b +  +  hx FF and ;

: READ  ( -- t h )
    0  begin   read)        \ Read sensor
        >r  dup chks        \ save & split reading
    r> <> while             \ Not ok?
        drop  1+            \ Drop reading, count retries
        dup 1- ?abort       \ More then one retry, abort
        2000 ms
    repeat
    nip  h-h ;              \ Split in temp. & hum.

: DHT22  ( -- )
    base @  decimal
    read  .dht ." %rel, " .dht ." Celcius " \ Show scaled result
    base ! ;

v: fresh
hex
chere swap - dm .
</code>