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I have been given the following scenario:

LED output:

• assume 200 communication codes per 24hrs, and that each of those LED code words take 20msec of processor time to communicate

BLE:

• connect to devices and then only communicate when it is time to send LED codes.

• use a menu traversal to re-start the link, BLE communicates the data to pass on the LED and when done LED comms to pass acknowledgement back to Smart Device.

            Idle Current        Active Current          On-Time (per day)   
LED             0                 30ma                 200 uses @ 20msec
BLE             0                 20ma                 201 uses @ 50msec
Processor    100uA                130ma                all the time

processor is 3v input
Battery should last 15days

Since rechargeables have approx. 80% capacity end of life and 80% capacity at -20oC. 

Therefore take Estimated battery as 60% of its rated value.

I am abit stuck in how I would calculate the estimated battery size in mAh, since the duty cycle is not given.

The duty cycle fomrula im am using is:

duty cycle% = (Ton/(Ton+Toff)) *100

duty c=  (200*20e-3 + 201*50e-3)/ ((200*20e-3 + 201*50e-3)+86400secs) *100

I'm getting a value of 0.46% which I'm not sure is right.

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1 Answer 1

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You want to calculate the power consumption in terms of Ah or mAh. This is how the battery is rated.

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  • \$\begingroup\$ yes but how will i go about calculating this \$\endgroup\$
    – Cherios
    Commented Apr 24, 2021 at 3:12
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    \$\begingroup\$ eg: LED 30mA 200 uses @ 20ms. 200 times 0.020 = 4 seconds per day or 200/24 * 0.02 = 0.166 seconds per hour 30mA times 0.166/3600 = 0.0014mAh repeat the calculation for the other loads. \$\endgroup\$
    – Kartman
    Commented Apr 24, 2021 at 3:27
  • \$\begingroup\$ how do i factor in the processor since its has an all time and idle current? \$\endgroup\$
    – Cherios
    Commented Apr 24, 2021 at 3:55
  • \$\begingroup\$ Calc the idle and active times separately. What fraction of an hour at 100uA and what fraction of an hour at 110mA? Eg: if the cpu was always idling at 100uA, then that would be 0.1mAh. \$\endgroup\$
    – Kartman
    Commented Apr 24, 2021 at 4:03
  • \$\begingroup\$ I am abit confused for "on all the time" since you cant always be idling and be active at the same time? is it safe just to assume 130mah + 0.1mah? \$\endgroup\$
    – Cherios
    Commented Apr 24, 2021 at 5:17

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