PICAXE and Perl join forces to send an email alert (via gmail) if there's a man down at home.
My daughter worries about me. I live 75 miles from her, out in the country, with no close friends or neighbors. So, partly to ease her concerns, but mostly because I like interesting projects, I decided to brew up a "Has Dad dropped dead?" application based on the computer that hosts this website, an old Windows XP PC sitting on a bench here in my lab/shop/studio. The machine, connected to a protected power source (UPS), runs 24/7. The server on the machine is Apache2, but it also has ActivePerl installed to help run some of the web applications. Perl can do lots of neat stuff and it's what makes this project feasible: It's already there and it's on all the time.
The keep-tabs-on-dad idea was to pick an often-used electrical device or appliance in the house (or multiple devices and/or appliances) and monitor it for activity (on/off operations) and report that activity, or more importantly lack of activity, to my daughter's smart phone via email. The 'device' chosen was the light in my bathroom.
Here's the Concept
Here's the series of events:
The envisioned system does not provide for instant emergency medical response (or instant anything). The goal is limited to reassuring the concerned individual that the monitored individual is up and about, not lying dead on the floor or otherwise incapacitated. And, if the monitored individual IS lying dead on the floor, the monitored individual will not be in an advanced state of decomposition by the time of eventual discovery. The as-built system has lived up to expectations.
The first issue was linking the monitored device, that is, getting the data from the monitored device, remote from the computer, to the computer. In this age of wireless everything I certainly didn't want to run wires. A pair of RF Digital's RFD21733 wireless transceivers, used in countless doorbells, garage door openers and keyless entry systems, seemed to be the way to go. The second issue was the logic and interface. Since I am somewhat familiar with the PICAXE 08M microcontroller, having incorporated the chip previously in a couple of projects interfacing the computer to external sensors (see Web server/PICAXE Interface and PICAXE Outside Temperature/Internet Project), and having a half-dozen on hand, decided to use the chip (it ended up being 2 chips) in the project to interface the computer.
RFD21733 and 08M
The RFD21733 is 15mm x 15mm (.6" x .6").
The Monitoring Circuit
(The transmit end of the monitor link.)
It could hardly be simpler. For this application, the RFD21733 is configured for "Mode 0" (by grounding all 'mode' pins; there are 8 modes (see RFD21733 data sheet). In this mode, when 3.3-volt power is applied, the transceiver immediately begins transmitting, in bursts every 2 seconds, its unique 32-bit ESN (Electronic Serial Number), encoded in such a way that the receive end, using an error-correcting algorithm, can decode in the presence of noise and interfering signals. The RFD21733 continues to transmit as long as power is applied. Power comes from a 5-volt USB charger, regulated to 3.3 volts through a series resistor and 3.3-volt zener diode. The RFD21733 is connected to the end of a USB cable (along with the voltage regulating components soldered to the underside), the cable plugged into the charger and the charger plugged into a spare light socket on the fixture. When the light is on, the socket is hot and the RFD21733 is transmitting. When the light is switched off, the socket goes dead and the RFD21733 stops transmitting. That's it!
Monitor Transmitter Schematic
Note: Pins 1, 2, 8, 9, 10, 12, 18, 19 are connected internally. Any of those can be used wherever a ground is required.
Underside of RFD21733
The white stuff is RTV silicone.
Connected to USB Cable
Mated to USB Charger
Plugged into Light Socket
The Monitor Receiver/Computer Interface
(The receive end of the remote monitor link.)
Another RFD21733 is used to receive the signal from the monitor transmitter, in this case configured for "Mode 5" (see RFD21733 data sheet). In this configuration, the transceiver outputs a 500mS positive-going pulse every 2 seconds as long as a valid signal is being received from the far end of the link. When the signal stops, the output stays low.
A couple of PICAXE 08M chips are used to detect receiver activity and convey it to the computer. 08M number one (#1) acts as a integrating timer and latch. The timer detects the presence of pulses from the receiver (RFD21733). "Activity" is reported only when a complete on/off cycle of the monitored appliance (the light) occurs. Thus, if the light is accidentally left on, the timer's output latch will not be set until such time as it is turned off. A light left on or off will eventually be reported as "No Activity". The second 08M (#2), when polled by the computer, reports the state of the timer's output latch and issues a pulse to reset the latch for the next occurrence. The idea here is not to count the times the light is switched on and off, but to report when it has not occurred within the sample interval.
And what if the power fails? Under certain conditions - the bathroom light left on, for example - a power failure and subsequent restoral might be misinterpreted as "normal activity". That it is not misinterpreted is based on the fact that power failures are not local. If the power fails in the bathroom, it also fails in the computer room. If the interface notices that power has failed, it ignores input from the remote and locks up in whatever state it happens to be in at the time. When power is restored, the interface resumes normal operation in its before-failure state (unless it happens to have been reset by the computer - the interface retains its ability to talk to the computer through a power failure).
Computer Interface Schematic
PICAXE 08M Pinout
Connections Underside of RFD21733
The thick wire on pins 9 and 10 serves as a counterpoise to the antenna. It improves antenna efficiency.
Completed Interface Board
The gray connector is a female DE9; it plugs into the computer's serial port. The red/black wire provides protected 5 volts DC; it plugs into one of the computer's power supply connectors. The USB connector plugs into an unprotected 5-volt power source. This could be a USB charger (as in Figure 1), but in this case it's connected to a USB port on another computer, not power-protected, next to the server. (The USB ports on computers are hot whenever they're plugged into a hot outlet and go dead when the outlet goes dead, regardless of whether or not the computer is running.)
Interface Board Attached to Computer
See also: Scheduling the Polling Interval starting below 'Firmware/Software'. ↓
Three programs are shown below, two for the 08M chips (in PICAXE Basic), and one for the Perl script that runs on the computer.
Copy the following code to the PICAXE Programming Editor and program the chip (works also on 08M2 chip):
'initializes on power up, pause 100 '100mS low 0 'sets remote signal LED (pin 7) to "not present" low 1 'sets activity (pin 6) to "no activity" b0 = 50 'sets accumulator count to 50 b1 = 0 'sets accumulator output to 0 b2 = 0 'sets cycle delay memory to 0 power_check: if pin3 = 1 then 'IF input 3 (pin 4) high, (this comes from PIC#2) low 1 ' resets output latch, (pin 6) low endif if pin2 = 1 then 'if input 2 (pin 5) high (high here indicates power OK) goto execute else pause 100 goto power_check endif execute: pause 100 'milliseconds, establishes sample rate at about 10 per second ReadADC10 4, W5 'reads voltage on input 4 (pin 3) from the RFD21733 receiver if W5 < 340 then 'less than about 1.65 volts, (half of 3.3 volts) b0 = b0 - 1 'discharges accumulator (b0), approx 20 second discharge (4 seconds on powerup) else b0 = b0 + 10 'charges accumulator; charge rate 10 times faster than discharge rate endif if b0 > 240 then 'limits max value b0 to 240 b0 = 240 endif if b0 < 10 then 'limits min value b0 to 10 b0 = 10 endif if b0 > 60 then 'accumulator output toggles high b1 = 1 high 0 'remote signal present, (pin 7) elseif b0 < 40 then 'accumulator output toggles low b1 = 0 low 0 'remote signal not present (pin 7) endif if b2 > b1 then 'this comparison looks for a 1 to 0 transition ("activity") high 1 'sets output latch ("activity detected") (pin 6) endif b2 = b1 'shifts contents of b1 to b2, retains the state of b1 for comparison in the next cycle goto power_check 'restarts check/sample/accumulate cycle
Copy the following code to the PICAXE Programming Editor and program the chip (works also on 08M2 chip):
main: serin 3, N2400, ("c="), b0 'waits here for input from computer, gets character after qualifier ("c=") if b0 = "d" then 'looks for "d" high 4 '(pin 3) lights "polling" LED if pin1 = 1 then 'gets input from latch, on pin 6 serout 0, N2400, ("1", 13) 'sends ASCII chr "1" to computer; 13 is CR, high 2 'sets output 2 high, resets latch in PIC #1 pause 200 '200ms low 2 'sets output 2 low else serout 0, N2400, ("0", 13) 'sends ASCII "0" to computer; 13 is CR endif pause 300 low 4 'extinguishes 'poll' LED endif goto main
Requires late-model ActivePerl installation
Copy the following code to your favorite text editor; edit the email message header (From:, To:, Cc:, Subject:) and body ($senddata) as appropriate; add your gmail account information (address and password), recipient addresses, and the path (c:/folder/etc) to the /time_ref.txt file (use forward slashes). Save the file (with .pl extension, eg, "monitor_dad.pl") to a location on the computer:
Scheduling the Polling Interval
This is done with "Scheduled Tasks" on older PCs (XP, etc) or "Task Scheduler" on later models, usually under "accessories" somewhere in the start menu. "Task" is set to the location of the Perl script on the computer (path\filename.pl); "start time" is set to midnight on some day convenient for the recipient (say, Friday); "repeat task" is set to the desired polling interval (12 hours, etc). Keep in mind that the "polling interval" is the time between polls of the interface. The "reporting interval" is the time between transmissions of the normal activity email.* If any polling interval passes with no activity, the program does not wait for the reporting inverval. The no activity email is immediately sent.
Schematics produced with DCCAD.
My cat Squish has been very helpful in getting details of the project published to the Web.
Here he is checkin' the prints..