I want to design a simple voltage indicator LED for my integrated circuit PIC18F4520.
No way to call this simple circuit (why complicate this easy circuit with uC?), and such purpose of this uC is waste.
This circuit can be simple only with few parts, and no uC.
1.what say about using a adc for this kind of situation..i.e. set a ref. voltage and make out the code for 4-5 leds..
2.what say about using a bar graph led for this...it may also appear gud...
This will do what you want.
Try a 5V1 for Z1 and a 3V9 for Z2. If a 5V1 is too high try a 4V7 in series with a germanium diode.
Linspire said:I have thinking of ATD, however my ATD's reference will based on the batteries source, which mean when batteries voltage drop down, the value of ATD will be different yields inaccurate indicator of voltage level.
Linspire said:I mean make a simple circuit for showing batteries voltage which supply to PIC.
Yes of course, a silly oversight on my part. Use a 2V7 zener for Z1 and don't put a germanium diode in series.Well, my green led use quite high voltage to light up the LED.
No, they're zener voltages. Model numbers will depend on the manufacturer. Search the net for "zener diodes" and you will find many links to stockists and they will list zener voltages vs model numbers.5V1, 3V9 are zener model no?
Furthermore, if you have a battery to supply your MCU, then why waste battery's energy on a led indicator? Keep the led off and when the battery falls below a specific voltage level, do something with the LED (let's say keep it of for 5 seconds and on for 200ms). Finally, you could choose a proper resistor to create a led current that will light the led, but as much as the human eye needs to see it during daytime or inside an enviroment with other lights on. In this way you will save battery life and indicate low battery when needed.
Linspire said:Are you trying to say the LED blinking will be turn on by a signal sent from the microcontroller.
Yes, since the MCU is there, why not use it like that?
The problem with the suggested analog (z-diode, transistor, LED forward voltage based) solutions is, that they have indistinct and temperature dependent thresholds and are additionally affected by type variations. They won't give much pleasure, I fear.
Utilizing the uP for voltage discrimination and selective display is basically a good idea, supposed it has free resources for this purpose. The problem of missing reference voltage can be easily overcome. At minimum, you can supply a zener diode stabilized voltage to an AN pin and measure VCC indirectly ( Vcc = Vref*1024/ADCvalue). Ultimately, use a stable shunt reference.
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