Hi, I've been looking into power efficient system designs lately and I've been wondering what method of communication takes the least amount of power for a 7-segment display and a 4x4 keypad? The methods I'm referring to are I2C, SPI, and direct pin communications.

Thanks!

 

Hi, I've been looking into power efficient system designs lately and I've been wondering what method of communication takes the least amount of power for a 7-segment display and a 4x4 keypad? The methods I'm referring to are I2C, SPI, and direct pin communications.

Thanks!

Are you concerned with 1 mA that flows when a button is pressed? Or are you talking about the power when a button is not pressed?

I don't think much energy is lost just charging the capacitance of the input pins in any of the communication options. Just limit the number of times you update.

If you are really concerned about energy, look at a 16x2 LCD display instead of LED 7-segment (assuming your 7-seg is LED.

 

Are you concerned with 1 mA that flows when a button is pressed? Or are you talking about the power when a button is not pressed?

I don't think much energy is lost just charging the capacitance of the input pins in any of the communication options. Just limit the number of times you update.

If you are really concerned about energy, look at a 16x2 LCD display instead of LED 7-segment (assuming your 7-seg is LED.

I'm talking about it overall, but the power it uses when it isn't pressed would be more important.

So would direct communication be the optimal choice for me?

I want to keep the 7-segment display since it fits my intended design more. Though I will definitely consider using an LCD display in future projects.

 

You need to specify what type of 7 segment display you are using. I have seen 7 segment displays the use LEDs (The most common.) Vacuum fluorescent display, filiment lamps, and liquid crystal. Is your display / keyboard device communicating with some other device using I2C / SPI ?

Les.

 

You need to specify what type of 7 segment display you are using. I have seen 7 segment displays the use LEDs (The most common.) Vacuum fluorescent display, filiment lamps, and liquid crystal. Is your display / keyboard device communicating with some other device using I2C / SPI ?

Les.

My 7-segment display uses LEDs. It's currently using I2C, but I'm wondering if I should change my communication method.

 

Your analysis appears faulty. As long as the 7-segment display consumes 90% or more of the power, small changes you make in other areas are like flyspecks in the pepper.

 

Your analysis appears faulty. As long as the 7-segment display consumes 90% or more of the power, small changes you make in other areas are like flyspecks in the pepper.

Oh okay, so ideally, I should get a more power efficient display like the previously mentioned 16x2 LCD display?

 

Oh okay, so ideally, I should get a more power efficient display like the previously mentioned 16x2 LCD display?

Yes and the next thing you must do for minimal power consumption is to update things as infrequently as possible. Power is consumed whenever CMOS inputs and outputs are beating up and down. Your circuits should be sleeping as much as possible.

If a microcontroller is involved, think about running your algorithms for a few milliseconds each time the watchdog timer expires and sleeps the rest of the time.

 

Yes and the next think you must do for minimal power consumption is to update things as infrequently as possible. Power is consumed whenever CMOS inputs and outputs are beating up and down. Your circuits should be sleeping as much as possible.

If a microcontroller is involved, think about running your algorithms for a few milliseconds each time the watchdog timer expires and sleeps the rest of the time.

In terms of updating things, my project is a electronic lock box, so I'd just update it whenever the user presses a button on the keypad right?

Do you have any microcontroller code examples that make use of the idea that you mentioned that you could show me?

 

In terms of updating things, my project is a electronic lock box, so I'd just update it whenever the user presses a button on the keypad right?

Do you have any microcontroller code examples that make use of the idea that you mentioned that you could show me?

Most have a "sleep" function and a "wake on interrupt". Usually one or more pins can interrupt.

A low power oscillator (e.g. onboard oscillator with a 32kHz tuning fork crystal) will consume as much energy as a wrist watch. The Microchip PIC microcontroller canndo this. I don't know about arduino - I have never tried to use one in a low power application.

The datasheet of a microcontroller you are familiar with is best place to check. Look for sleep, and wake commands.

 

Using an Atmel processor you would go the the AVRFreaks website
Using a PIC you would go to the Microchip forums

 

So back to the topic question, if I switch to the LCD display, what communication method would be ideal?

Also, would directly connecting the keypad without I2C or SPI be ideal in terms of power?

 

So back to the topic question, if I switch to the LCD display, what communication method would be ideal?

Also, would directly connecting the keypad without I2C or SPI be ideal in terms of power?

The LCD uses power for backlight but you can turn that on only when you need it.

You can use EEPROM (already a feature available on a microcontroller) to set your combination then you can turn the whole thing off. Then turn it on when you want to enter a combination to open the safe. If you go the eeprom / shutdown method, you can have any display you want because it will only use power for the minute or two that you are opening and closing the box.

 

The LCD uses power for backlight but you can turn that on only when you need it.

You can use EEPROM (already a feature available on a microcontroller) to set your combination then you can turn the whole thing off. Then turn it on when you want to enter a combination to open the safe. If you go the eeprom / shutdown method, you can have any display you want because it will only use power for the minute or two that you are opening and closing the box.

That sounds like a good option. I was already thinking about adding a circuit with a button to provide power for around a minute.

Overall though, communication methods aren't very crucial for my project due to how rarely the devices communicate with one another, right?

 

That sounds like a good option. I was already thinking about adding a circuit with a button to provide power for around a minute.

Overall though, communication methods aren't very crucial for my project due to how rarely the devices communicate with one another, right?

Correct.

Use a microcontroller with plenty of pins.
You'll need 4-pin parallel connection for a standard 16x2 display (some with SPI adapters are available) plus one for back light and enable pins.

You'll need some for the keypad (depending on connections) and how you plan to scan them or just have direct connections for the 16 keys (depends on your keypad)