WiFi Pinger





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.



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    What is a wifi pinger?

    great , need more infos about how you did the charger !

    and mabe a shield for arduino ?

    Friends, I have been thinking of making a beacon chip for quite some time, see my blog on the topic: http://mobimation.blogspot.se/2011/10/wifi-beacon-chips.html?showComment=1372549170668
    The point is to manufacture very inexpensive chips with small power requirements that do nothing else than transmit a Wifi beacon.
    That way the environment could be blessed with having such beacons placed at locations where it is otherwise impossible to get a location indication, such as underground, subways or some shopping malls for example. Complete Wifi chips are in many cases too expensive for the purpose.
    If any of you want to collaborate with me to drive a project on what a beacon design would take you are welcomed. One question to clear up is if there are frequency band restrictions that forbid anything else than certified full Wifi standard chips to operate in that band.

    Thanks for your mail - your chips would have been great when I was designing this! Sadly at this time I don't think they would work with an iPhone (Apple block access to the data needed to recognise the WiFi signature) but they should be ok with an Android phone.
    It looks as if WiFi fingerprinting may become a common way of finding indoor location (google "WiFiSLAM"). IF Apple do include this feature in a future version of iOS then low power WiFi beacons will be really useful (and in great demand).
    I can't help with the certification question - but the 2.4GHz band is used for a whole bunch of different applications (though the 5GHz WiFi band would be better for location purposes).

    This could also be used to verify an open wifi connection, Unlike the wifi detectors, that scan for a signal on wifi, You can use this to be sure you can get on wifi, Rather then find it locked.

    Appears that you should have called the device a beacon and left it that. :) naming it a pinger confuses A ping is generally sent to a target, with a response from the taget expected. Beacons are generally broadcasts that can be received by multiple stations, even if only 1 or more can make use of the data broadcast,  response from a receiving station may not be expected.  Then again it may be HP fault for first calling something that's not a ping a ping

    Hi, I'm looking to make a similar project (very similar). All I need to do is broadcast a pre-configured SSID. No traffic, just the SSID as a kind of 'hey I'm on' deal. I'm trying to find a retailer for your S103 WLAN module used, but can't find it on the recommended sites. Does ANYONE (not just pyxis) know of any other brands that might help me out? --Davedwin

    .;dHmm... It'd be pretty cool to make an SSID 'spammer'. ;P

    Already exists, at least a software version. Its called MDK3. Its only available for a Linux-based OS, though. The SSID "spammer" you're looking for is more commonly referred to as "beacon flooding". Check out MDK3, it has sooo many cool modes. I think you'll like it.

    I actually found this feature in Metasploit. Problem is that the wireless card needs a certain chipset (that I don't have) or to get an expensive external card.