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Battery powered AT89S52 device...is it feasible??

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seemanta

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at89s52 power usage

Hi,

I have been prototyping a small project of mine based on the AT89S52 for sometime now. Now as I am nearing completion I am thinking of the power consumption issues I might have with the finished stuff, which will run on battery power.

Till now, I was prototyping using an evaluation board which runs on a 5 VDC power supply. So I did not have any power consumption issues.

However, in a few days time when I would be creating a battery powered version
of my project, how will it be w.r.t the power consumption?? Any prior experience from any one of you folks out here?

I am planning to use 4x1.5 VDC cells in series to get about 6 Volts. My project runs an RTC and an LCD. Basically it is a digital clock based on the 89S52 micro.

I was also thinking of adding a temperature display based on the DS18S20 temperature sensor. Will it be overkill?

If anyone in EDABOARD has the experience of using AT89S52 for battery powered applications before, then I would be grateful to know how it performs w.r.t power consumption.

regards,
Seemanta

P.S. I searched in ATMEL website and discovered that there is a AT89LP series which offer single cycle execution and low power, but after making some enquiries I realized that unfortunately LP series is not available in India(Hyderabad) till now. Duh! :(
 

laktronics

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Hi,
One sure method of power saving is the usage of idle mode and even better Sleep mode. But Sleep mode requires a Reset to be generated and you must have two routines to distinguish between Cold Reset and Warm Reset. Idle mode is easier, but power consumption is more than in Sleep mode, it reqires only an interrupt to take out of idle mode. Since your applicatin is for clock and temperature display, you can infact program the RTC for 1sec. interrupt and after finishing all routines go to idle mode. Even your temperature sampling can be made once in a second. You should generate interrupt from Time/Alarm setting switches also for faster response to these switch operations.
Regards,
Laktronics
 

rajeshkumar123

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Hi,

The feasibility also depends on the battery chemistry. Can u answer me a few questions on your projects.

1) what is the average current consumption of ur circuit?

2) Are there any limitations on the size of your product which demands the battery to be very compact?

3) What is the type of battery u are presently using?
 

ldanielrosa

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How long do you need it to last on one set of batteries? If you have pins to spare, you can control power to the accessories (LCD, sensor). The RTC may have it's own battery, but you should keep it powered when you can. The uC probably only draws a few mA.
 

laktronics

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Hi,
Further to my previous post, please note that 89S52 allows recovery from sleep mode using external interrupts, which makes your job easy, you do not have to worry about handling two types of resets as in the case of its predecessors.
Regards,
Laktronics
 

seemanta

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ldanielrosa,
Can you please explain what you mean by using a few free pins to control the power consumption of the LCD and the temperature sensor? And yes, I am powering the RTC, even though it has its own battery inside. This would mainly keep the time from drifting, since the drift is much more pronounced when the RTC is powered internally.

rajeshkumar123,
I am planning to use 4 AA sized batteries to generate a total of 6 volts.
Will using 3 AA batteries work? Given that, that would only generate 4.5 volts.
I have not yet tried that option but your opinion would be very useful.

And yes, I do not have a limitation of size very much. I can easily pack 4 AA sized batteries for this project.

As for the average current drawn by my project, I am not sure. I just have to sit once and work out the average current drawn. Will let you know once I do that.

laktronics,
Thanks for your suggestion. I was using the idle mode, but now I shall switch over to PD mode. I also read the AT89S52 data sheet and it seems indeed an external interrupt can take it out of PD mode.


And all,
Many thanks to all of you for answering my queries so patiently! :D

regards,
Seemanta
 

rajeshkumar123

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HI,

You dont need to work out the average power consumption. Just put a Multimeter in series with the battery and your circuit to measure current in two below conditions

1) With all pheripherals active

2)In sleep mode.


calculate average current by taking an average of the two if the duty cycle(time in active modedivided by the sum of time spent in active and sleepmode) is 50%.
Else calculate average current according to ur duty cycle.


if Your battery capacity of AA might me around 2500mAh and if your average current(duty cycle taken into consideration) comes around say 50mA then ur circuit will have a standby time of 50 Hrs (theoretically).
 

mayankatacadence

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Try using a DC-DC up converter. There are plenty in the market. You can get free samples from MAXIM-IC. But you will need SMD soldering skills to use most of these chips. They can boost the supply voltage as low as .7 volts (1 NiMH) to 5Volts fixed voltage at 100mA+ at >80% efficiency. You should be able to get 20hrs on a single high capacity NiMH AA cell.
 

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