hi j,
Have you calculated how long that battery will power a 14uA load.
E
EDIT:
http://batteryuniversity.com/learn/article/elevating_self_discharge

Update:
I would say @Bordodynov circuit in the thread link, post #7 will give the required 4 hour delay.

Calculating to a discharge of 2.4 volts would give me 6 years of battery life.
I'll look into that chip.
Thanks

 

hi J,
Are you in the UK.?
E

EDIT:
OK, was going to suggest some components sources in the UK.

 

hi J,
Are you in the UK.?
E

No... US, Florida

 

Normally I would recommend a circuit based on the CD4060 oscillator/counter for such a long timing period. However, a 14 bit divider functions as only 13 bits of delay. 4 hours is 14,400 seconds, so the oscillator period would be 1.75 s, or a frequency of 0.57 Hz. That makes for a relatively large timing capacitor, and a charging current that is close to the leakage current. The CD4541 (16 bit) is 4x better, but the champ is the CD4521 (24 bit) oscillator/divider, and it has an ultra low power oscillator section. Now the osc freq is around 580 Hz, much easier to implement and adjust. In stock at Digi-Key for 56 cents.

The basic idea is that applying and removing a reset signal zeros out the counter. For the next 8,388,607 oscillator cycles, the 24th bit output is low. On the next cycle it goes high, signalling the end of the 4 hour delay. Adjusting the oscillator freq tunes the delay period.

ak

 

John's post#14 looks good as well. This might be better since I don't have to worry about programing a chip.

Note that the max delay period is 2 hours.

ak

 

what is your transmitter draw?

I have recently completed a similar project, with battery life paramount. It's a bit more involved, but may give some consideration. My system consisted of the PIR element with lens, amplifier, window comparator, and a digipot to vary amplifier gain and width of window. An Atmel AT328 drove the I2c pot, as well as sensed the PIR output. On wake, from PIR interrupt, the micro would do some due diligence, power up the transceiver, send a packet of info, wait for confirmation, shut down transceiver power, possibly do some local logging, cleanup, then sleep. If your micro is doing the 4 hour delay, your sleep current is higher. I kept the PIR circuit always active, but you could power down the trans and PIR supply via a switching power supply enabled my the micro