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local sds011 = {}
local c_head = 0xaa
local c_tail = 0xab
local c_id = 0xb4
local c_read = 0x00
local c_write = 0x01
local c_report_mode = 0x02
local c_active = 0x00
local c_passive = 0x01
local c_query = 0x04
local c_sleepcmd = 0x06
local c_sleep = 0x00
local c_work = 0x01
local c_workperiod = 0x08
sds011.work_period = nil
sds011.active_mode = nil
function sds011.finish_cmd(cmd)
cmd = cmd .. string.char(0xff, 0xff)
local checksum = 0
for i = 3, string.len(cmd) do
checksum = (checksum + string.byte(cmd, i)) % 256
end
cmd = cmd .. string.char(checksum, c_tail)
return cmd
end
function sds011.query()
local cmd = string.char(c_head, c_id, c_query)
cmd = cmd .. string.char(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
return sds011.finish_cmd(cmd)
end
function sds011.set_report_mode(active)
local op = c_write
local cmd = c_passive
if active == nil then
op = c_read
active = false
elseif active then
cmd = c_active
end
local cmd = string.char(c_head, c_id, c_report_mode, op, cmd)
cmd = cmd .. string.char(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
return sds011.finish_cmd(cmd)
end
function sds011.sleep(sleep)
local cmd = string.char(c_head, c_id, c_sleepcmd, c_write)
if sleep then
cmd = cmd .. string.char(c_sleep)
else
cmd = cmd .. string.char(c_work)
end
cmd = cmd .. string.char(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
return sds011.finish_cmd(cmd)
end
function sds011.set_work_period(period)
-- period == 0 : continuous operation, about one measurement per second
-- period > 0 : about one measurement every <period> minutes, fan is turned off in-between
if period ~= nil and (period < 0 or period > 30) then
return
end
local op = c_write
if period == nil then
op = c_read
period = 0
end
local cmd = string.char(c_head, c_id, c_workperiod, op, period)
cmd = cmd .. string.char(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
return sds011.finish_cmd(cmd)
end
function sds011.parse_frame(data)
local header, command, pm25l, pm25h, pm10l, pm10h, id1, id2, sum, tail = struct.unpack("BBBBBBBBBB", data)
if header ~= c_head or (pm25l + pm25h + pm10l + pm10h + id1 + id2) % 256 ~= sum or tail ~= c_tail then
return false
end
if command == 0xc0 then
local pm25 = pm25h * 256 + pm25l
local pm10 = pm10h * 256 + pm10l
sds011.pm2_5i = pm25 / 10
sds011.pm2_5f = pm25 % 10
sds011.pm10i = pm10 / 10
sds011.pm10f = pm10 % 10
return true
elseif command == 0xc5 and pm25l == 0x02 then
sds011.active_mode = pm10l == 0
return true
elseif command == 0xc5 and pm25l == 0x08 then
sds011.work_period = pm10l
return true
end
return false
end
return sds011
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