Some More Help - JDM Programmer & 16F877A power consumption

Discussion in 'Embedded Systems and Microcontrollers' started by chileflora, Jul 22, 2009.

  1. chileflora

    Thread Starter New Member

    Jul 11, 2009
    7
    0
    I have two issues to solve:

    I made a JDM programmer which works fine, but its voltages are somewhat beyond the values permitted for the 16F877A, namely, low DATA and CLOCK are about -0.6 V when the processor is connected (-1 V without processor), and about 5.8 V for HIGH, with the supply voltage around 5.2 V. Programming Voltage is around 13.5 V. In the data sheet a maximum of -0.3 V and +0.3 V above VDD is permitted.

    Question: is this normal for JDM? Could it affect the reliability of the processors? I am not getting any errors, but the idea is to use these processors as loggers which should work for several months unattended.


    In the data sheet for 16F877A for 4 MHZ 5V a current of 1.5 mA is given. I am getting a reading of about 6 mA (processor doing a Loop, with everything off). The circuit I am using is a very simple one, a digital thermometer chip DS1820 (which has a standby current of 1 uA), crystal, and two indicator LEDs. Since the device is intended to work for about 3 months on rechargeable batteries, the difference between 1.5 and 6 is huge. Can someone give a hint as to what can be done to reduce the power consumption. I have tried two different processors and it is the same story.

    I have left the unused pins of the 16F877 floating and by default as inputs, RB internal pull-up resistors are disconnected. I assume that floating inputs would not affect the power consumption?
     
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    remove the led's. they typically require from a few to 20 ma each. do not float inputs it can actually destroy the chip and could use current.
     
  3. chileflora

    Thread Starter New Member

    Jul 11, 2009
    7
    0
    Thanks for the tips. The LEDs are obviously turned off. I assume that setting TRIS as output does not increase consumption if the pins are set to LOW.
     
  4. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Not sure if high or low uses current, but outputs are ok to float, and you should, I think.
     
  5. chileflora

    Thread Starter New Member

    Jul 11, 2009
    7
    0
    Thanks again,

    I have set all unused pins to output LOW, and got 1.2 mA consumption at 5.5 V, down from 5 mA!
     
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