1 files changed, 74 insertions, 0 deletions
diff --git a/sds011.lua b/sds011.lua
new file mode 100644
index 0000000..a528720
--- /dev/null
+++ b/sds011.lua
@@ -0,0 +1,74 @@
+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
+
+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.set_report_mode(active)
+	local cmd = string.char(c_head, c_id, c_report_mode, c_write)
+	if active then
+		cmd = cmd .. string.char(c_active)
+	else
+		cmd = cmd .. string.char(c_passive)
+	end
+	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 < 0 or period > 30 then
+		return
+	end
+	local cmd = string.char(c_head, c_id, c_workperiod, c_write, 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 command ~= 0xc0 or (pm25l + pm25h + pm10l + pm10h + id1 + id2) % 256 ~= sum or tail ~= c_tail then
+		return nil
+	end
+	pm25 = pm25h * 256 + pm25l
+	pm10 = pm10h * 256 + pm10l
+	return pm25 / 10, pm25 % 10, pm10 / 10, pm10 % 10
+end
+
+return sds011