Introduction: WiFi Pinger
A Pyxis Design Project.
This instructable describes an RF beacon using WiFi - we call it a 'Pinger'. It is intended to be used as an alternative to, or to complement, GPS in location based applications. The 'WiFi Pinger' has been specifically designed to operate with the mediascape software described here (nb still under development April 2008). An early application using similar non-WiFi technology is described in this press release.
The Pinger uses a WLAN Compact Serial Module to transmit a pre-configured beacon signal as part of the WiFi standard. It can thus be recognised by any WiFi equipped device. It is compact and low powered and has an (approximately) omnidirectional radiation characteristic. We use it to identify (or tag) places, people or objects enabling recognition by mobile receivers such as WiFi equipped PDAs or cellphones.
The range of the Pinger is around 100m outdoors - and it's intended that the mscaper software will be able to be set for short, medium or long range. It can be powered and/or charged from a USB source - its battery life is over 12 hours.
Step 1: Parts List
To build a WiFi Pinger you'll need the following (mostly from RS ):-
1 x 0.22 ohm resistor (RS 135-500)
1 x 47uF 6.5v capacitor (RS 547-9732)
2 x 10uF 10v capacitors (RS 547-9776)
3 x MBRA140 Schottky diodes (RS 625-5650)
1 x flashing red LED (RS 228-6032)
1 x FMMT717 pnp transistor (RS 215-6515)
1 x LM3622 LiPoly charger IC ( DigiKey )
1 x USB socket (RS 515-2011)
1 x 4 way Molex 1.25mm socket (RS 279-9285)
1 x 12 way Molex plug case plus leads (RS 319-1042 & 279-9544)
1 x on/off switch (RS 334-268)
S103 WLAN Compact Serial Module ( RF Solutions (UK) or Datahunter (US) )
pcb from expressPCB (or pyxisdesign) (pcb shown below and file attached)
1 x dual PLF423566-S Varta LiPoly battery (RS 457-8282)
Hammond case (RS 613-8319)
... and tools for surface mounting soldering.
Step 2: Schematic
Here's the circuit diagram :-
Step 3: Build
Here's a sequence of photos showing how to assemble the Pinger - this is where you build-it-yourself!
Step 4: Adaptor
Before using the pinger, you'll need to configure it - this requires a special adaptor lead.
The schematic is below and a photos of the build process are in the next steps ....
Step 5: Adaptor Build
Here are the parts required (and RS Stock Nos) :-
1 x Molex 4 way plug plus leads (279-9162 & 279-9544)
1 x DS276 RS232 level convertor (138-297)
1 x 10uF 16v capacitor (538-1922)
1 x BAT41 Schottky diode (544-4679)
1 x 9w 'D' type plug (female) and enclosure (544-3749 & 425-7755)
and a 1.1" x 0.6" piece of stripboard
The assembly process is shown in the images. Do make sure you get the polarities of the capacitor and diode correct!
Step 6: Configure
You'll need to connect the Pinger to a PC running Hyperterminal using an RS232 cable and the adaptor. Set the terminal to 38,400 baud 8-N-1.
After connection, on powering up the S103, the backspace key should be repeatedly pressed until 'Command' appears on the terminal screen. The following commands should then be entered to configure the pinger:-
Mode A (sets Ad-hoc mode instead of infrastructure)
SSID Pinger_xxxx (sets SSID (name) to Pinger_xxxx)
Chan x (sets channel to x where x = 1 to 11 (US) 1 to 13 (EU))
PSMode 1 (switches on power saving)
SE (save and exit)
Settings can be confirmed by entering the first word of the command.
Once the Pinger is configured you're ready to go. Connect it to a USB host to charge the battery, then turn it on and look for pings! A fully charged Pinger should run for over 12hrs - it'll need around four hours to recharge.