add support for reading the work period from the sensor

3 files changed, 44 insertions, 20 deletions

diff --git a/README.md b/README.md
index b38159c..1f3c839 100644
--- a/README.md
+++ b/README.md
@@ -46,12 +46,14 @@ port = softuart.setup(9600, 2, 1)
 port:on("data", 10, uart_callback)
 
 function uart_callback(data)
-	local pm25i, pm25d, pm10i, pm10d = sds011.parse_frame(data)
-	if pm25i ~= nil then
-		-- pm25i/pm10i contain the integer part (i.e., PM2.5 / PM10 value in µg/m³)
-		-- pm25d/pm10d contain the decimal/fractional part (i.e., PM2.5 / PM10 fraction in .1 µg/m³, range 0 .. 9)
-	else
-		-- invalid checksum or non-data frame (i.e., acknowledgment of a write command)
+	if sds011.parse_frame(data) then
+		-- PM values or work period have been updated
+		if sds011.pm2_5i ~= nil then
+			-- pm2_5i/pm10i contain the integer part (i.e., PM2.5 / PM10 value in µg/m³)
+			-- pm2_5d/pm10d contain the decimal/fractional part (i.e., PM2.5 / PM10 fraction in .1 µg/m³, range 0 .. 9)
+		else
+			-- sds011.work_period has been updated after using sds011.set_work_period
+		end
 	end
 end
 ```
@@ -68,6 +70,7 @@ Currently, the following commands are supported
   * sleep == true: put sensor into sleep mode. The fan is turned off, no further measurements are performed
   * sleep == false: wake up sensor.
 * `port:write(sds011.set_work_period(period))`
+  * period == nil: request current work period; does not change it
   * period == 0: continuous operation (about one measurement per second)
   * 0 < *period* ≤ 30: about one measurement every *period* minutes; fan turned off in-between
 
diff --git a/init.lua b/init.lua
index 51aeafc..6dc32d0 100644
--- a/init.lua
+++ b/init.lua
@@ -25,12 +25,13 @@ end
 function setup_client()
 	print("Connected")
 	gpio.write(ledpin, 1)
+	port = softuart.setup(9600, 2, 1)
+	port:on("data", 10, uart_callback)
 	publishing_mqtt = true
 	mqttclient:publish(mqtt_prefix .. "/state", "online", 0, 1, function(client)
 		publishing_mqtt = false
+		port:write(sds011.set_work_period(nil))
 	end)
-	port = softuart.setup(9600, 2, 1)
-	port:on("data", 10, uart_callback)
 end
 
 function connect_mqtt()
@@ -55,8 +56,7 @@ function connect_wifi()
 end
 
 function uart_callback(data)
-	local pm25i, pm25f, pm10i, pm10f = sds011.parse_frame(data)
-	if pm25i == nil then
+	if not sds011.parse_frame(data) then
 		print("Invalid or data-less SDS011 frame")
 		return
 	end
@@ -64,8 +64,14 @@ function uart_callback(data)
 	if sds011.work_period > 0 then
 		work_period = string.format("%d min", sds011.work_period)
 	end
-	local json_str = string.format('{"pm2_5_ugm3": %d.%d, "pm10_ugm3": %d.%d, "rssi_dbm": %d, "period": "%s"}', pm25i, pm25f, pm10i, pm10f, wifi.sta.getrssi(), work_period)
-	local influx_str = string.format("pm2_5_ugm3=%d.%d,pm10_ugm3=%d.%d", pm25i, pm25f, pm10i, pm10f)
+
+	local json_str = string.format('{"rssi_dbm":%d,"period":"%s"', wifi.sta.getrssi(), work_period)
+	if sds011.pm2_5i ~= nil then
+		json_str = string.format('%s,"pm2_5_ugm3":%d.%d,"pm10_ugm3":%d.%d', json_str, sds011.pm2_5i, sds011.pm2_5f, sds011.pm10i, sds011.pm10f)
+		local influx_str = string.format("pm2_5_ugm3=%d.%d,pm10_ugm3=%d.%d", sds011.pm2_5i, sds011.pm2_5f, sds011.pm10i, sds011.pm10f)
+	end
+	json_str = json_str .. '}'
+
 	if not publishing_mqtt then
 		watchdog:start(true)
 		publishing_mqtt = true
diff --git a/sds011.lua b/sds011.lua
index dc0004f..98f5b09 100644
--- a/sds011.lua
+++ b/sds011.lua
@@ -55,23 +55,38 @@ 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
+	if period ~= nil and (period < 0 or period > 30) then
 		return
 	end
-	sds011.work_period = period
-	local cmd = string.char(c_head, c_id, c_workperiod, c_write, period)
+	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 command ~= 0xc0 or (pm25l + pm25h + pm10l + pm10h + id1 + id2) % 256 ~= sum or tail ~= c_tail then
-		return nil
+	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
+	end
+	if command == 0xc5 then
+		sds011.work_period = pm10l
+		return true
 	end
-	pm25 = pm25h * 256 + pm25l
-	pm10 = pm10h * 256 + pm10l
-	return pm25 / 10, pm25 % 10, pm10 / 10, pm10 % 10
+	return false
 end
 
 return sds011