March 19, 2014

Connection guide for the Wireless Multi-sensor

Here are the different connections to the Wireless Multi-sensor version 1.1.

First I start with presenting the different ways to connect sensors,

  • Temperature and Temperature/Humidity sensors
  • PIR and COsensors
  • Passive switch-type of sensors

In the end I show how you can power the Multi-sensor and where you can feed it, under the section Power.

Temperature and Temperature/Humidity sensors

The 1-wire network is ideally a straight bus. But it could as well be pure star-shaped. This shape is however not recommended by Maxim. For more detailed information about the network topology I recommend reading Guidelines for Reliable Long Line 1-Wire Networks.
A network length of about 50 meters have been reported to work OK with the Multi-sensor, but do not see this as the maximum limit. Maximum network length is still to be found. Cable type is important if you plan to build a large network. Pair-twisted EKKX 2x2x0,5 is one of the recommended cables to successfully build a large working 1-wire network.

The following 1-wire sensors have been verified to work, DS18B20, DS18S20, DS18B22, DS1820 and MAX31820.

With the DS2423-firmware the Multi-sensor will support the DS2423-2-channel counter commonly used when logging energy consumption. however there is a simpler way.

The DHT22 can be connected with up to 100m cable according to the specification.

PIR or CO2 sensor

You can choose from many different types of sensors to connect to the PIR-input. Any of those types (or similar) can be connected right into the pin connector after removing the read jumper thing.

Passive switch-type of sensors

Any passive switch-type of sensor can be connected to the PIR-input. With this type of sensor you will need to add a Pull-down resistor to force the DATA-line low when the switch is open. The pull-down resistor should have a value of about 4k7 to 10kOhm, but it is not critical.
A transmission will only be done as soon as the DATA-line goes high.


You can power the Multi-sensor in one of two ways. Either you use the USB-port, or you use the solder pads on the PCB marked BAT for battery, to power it with the power source of your choice.
The table below will guide you with what minimum and maximum voltages that are allowed.

The numbers within the parenthesis are the maximum ratings for each sensor. However, the PIC-microprocessor limits the maximum voltage to 5.5V. I have tested it successfully with 6.5V, but that is outside the PIC12F675 specification and not recommended.

You will be safe to feed the Multi-sensor with 4.5-5.5V independently of which sensors you combine. The easiest way is to use a USB-charger or similar. The USB port is only there to give power to the Multi-sensor. The D+ and D- pins are not used.

If you want to minimise the form factor you will likely want to choose a small battery. It can be useful to know that you can go as low as 3.0V as long as you only use 1-wire DS18X20 sensors. I have successfully powered a Multi-sensor and one DS18B20 with a CR2032 cell battery (3V). The test was speed up with increased transmission interval. The estimated lifetime of this configuration is estimated to more than 1.5 years.

The transmitting range of the Multi-sensor will depend on the voltage level.
Here is the specification for the Radio module used in the Multi-sensor (FS1000A):
Operating Voltage2.5 V to 12 V
Operating Current4mA @ 5V, 15mA @ 9V
Quiescent Current10uA
Operating Temperature-10C - 60C
Max. Data Rate2.4K
Data InputTTL
RF Power20 mW@5V

For the advanced user it could probably be possible to boost the transmission range by feeding the RF module with 12V separate from the rest of the Multi-sensor.

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