Main

Length of Cable		(Feet)  or		(Meters)
Load Current		(Amps)
Source Voltage		(DC Volts)
	Calculate

	Size		Diameter		Resistance @ 77 F		Resistance for length (Ohms)	Voltage Drop (Volts)	Output Voltage (Source less Drop)	Percentage Loss (%)
	AWG	Metric mm2	inch	mm	ohm/1000'	ohm/km
	24	0.205	0.0232	0.590	26.1823	85.900
	22	0.326	0.0293	0.744	16.4592	54.000
	20	0.518	0.0369	0.938	10.3632	34.000
	18	0.823	0.0465	1.182	6.5227	21.400
	16	1.309	0.0587	1.491	4.0843	13.400
	14	2.081	0.0740	1.880	2.5756	8.450
	12	3.309	0.0933	2.371	1.6215	5.320
	10	5.261	0.1177	2.989	1.0180	3.340
	8	8.366	0.1484	3.770	0.6401	2.100
	6	13.302	0.1871	4.753	0.4023	1.320
	4	21.151	0.2360	5.994	0.2533	0.831
	2	33.631	0.2976	7.558	0.1594	0.523
	1	42.408	0.3341	8.487	0.1265	0.415
	1/0	53.475	0.3752	9.530	0.1003	0.329
	2/0	67.431	0.4213	10.702	0.0796	0.261
	3/0	85.029	0.4732	12.018	0.0631	0.207
	4/0	107.219	0.5313	13.495	0.0500	0.164

openhab.conf , conenction to mosquitto

mqtt:mysensor.url=tcp://10.0.1.10:1883
mqtt:mysensor.clientId=MQTT
mqtt:mysensor.qos=0
mqtt:mysensor.retain=true
mqtt:mysensor.async=false

Some of these modules come with pins soldered in that top right corner, so you don’t have to solder anything. You would simply connect a jumper wire to that pin that is highlighted in red (see Figure below). With my particular sensor I had to solder a small wire.
Here’s how it looks, now if you supply 3.3V through that red wire your module works at 3.3V.

Filesystem on a USB stick (Rootfs on External Storage / extroot) first we need to install basic USB support for EXT4 and FAT32 formatted USB sticks

root@OpenWrt:~# opkg update
root@OpenWrt:~# opkg install kmod-usb-storage block-mount kmod-fs-ext4 kmod-fs-vfat
kmod-nls-cp437 kmod-nls-cp850 kmod-nls-iso8859-1 kmod-nls-iso8859-15 kmod-scsi-core
e2fsprogs fdisk

check if the USB stick was recognized

root@OpenWrt:~# ls /dev/sd*

you should see one or more devices like sda1, sdb1, sdb2, … partition the USB stick

root@OpenWrt:~# fdisk
Command (m for help): m (displays actions)
Command (m for help): p (display partition table)
Command (m for help): d (delete partion - had only 1 on my stick)
Command (m for help): n (new partition)
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-621, default 1): RETURN
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-nnnn, default nnn):
Command (m for help): a (make partition bootable) RETURN
Partition number (1-4): 1 Command (m for help): w (write to disk)

format USB stick with ext4 filesystem

root@OpenWrt:~# mkfs.ext4 /dev/sda1

mount the USB stick and copy the flash /overlay to the USB stick

root@OpenWrt:~# mkdir -p /mnt/usb
root@OpenWrt:~# mount -t vfat /dev/sda1 /mnt/usb
root@OpenWrt:~# tar -C /overlay -cvf - . | tar -C /mnt/usb -xvf -
root@OpenWrt:~# vi /etc/config/fstab

the ‘config mount’ block should look like this

config 'mount'
        option target   /overlay
        option device   /dev/sda1
        option fstype   ext4
        option options  rw,sync
        option enabled  1
        option enabled_fsck 0

restart the router and check if everything’s ok

root@OpenWrt:~# df
Filesystem           1K-blocks      Used Available Use% Mounted on
rootfs                 1962212     65100   1798716   3% /
/dev/root                 1536      1536         0 100% /rom
tmpfs                    14600        72     14528   0% /tmp
tmpfs                      512         0       512   0% /dev
/dev/sda1              1962212     65100   1798716   3% /overlay
overlayfs:/overlay     1962212     65100   1798716   3% /

powered by power supply module (lm2596)

• 2x connectors for Dallas temperature sensor
• 1 - photocell connector (light sensor)
• 1 DHT-22 connector (humidity and temperature)
• 1 connector for pir sensor (HC-SR501 PIR Motion Sensor Module)
• 1 connector for Relay (led light controller )
• 1 conenctor for Magnetic Door Switch Sensor
• 1 conenctor for power out (5v)

(this version has a 1117 3.3v regulator and 7805 5.0v)

• -is connected directly to the battery
• 2x connectors for Dallas temperature sensor
• 1 - photocell (light sensor)

(this version is reporting the battery level)

• 2x connectors for Dallas temperature sensor
• 1 - photocell connector (light sensor)
• 1 DHT-22 connector (humidity and temperature)
• 1 connector for pir sensor (HC-SR501 PIR Motion Sensor Module)
• 1 connector for PWM IRF3205 (led light controller )
• 1 conenctor for Magnetic Door Switch Sensor
• 1 conenctor for power out (5v)

(this version has a 1117 3.3v regulator and 7805 5.0v)