Powering a chip that calls for Vcc of 5v

Can I use 4 NiMH batteries that will provide 4.8 -5V roughly to power a chip that needs 5V?

The battery voltage might drop as it get discharged. I wonder how much it will affect the chip performance? I'm talking about the ATtiny85.

Thanks

You should be fine till ~4 volts.
This can be check for absolute minimum range with a variable power supply.

If you are concerned, you could feed a boost SMPS converter to get everything out of the batteries as possible.
These converters can be found on eBay, Pololu etc.

.

The ATtiny85 will run on voltages as low as 2.7 V.

However, you have to lower the clock speed (crystal) to run at lower voltages. Consult the data sheet.

Simply use the bootcode for 1MHZ.

You will not even need a quartz. Just use internal timing.

1 Mhz is good enough for most tasks.

If you need more performance you simply need more power.

jremington:
The ATtiny85 will run on voltages as low as 2.7 V.

1.8 V for the ATtiny85V processor. Which is conveniently “about dead” for two common primary cells.

They actually function at 1.6 V but that is definitely outside the voltage range for reliable operation.

Thanks

I also want to use said power supply (4 AA NiMH) to power a 28 byj 48 stepper motor. The motor needs 5V-16V I think. Even at the highest voltage of the battery, it probably won't power the motor sufficiently.

I can use more batteries for higher voltage (for the motor), but that will make the voltage too high for the Atiny85 I'm afraid.

What's the best way around this?

The goal is to have a common power supply for both the microprocessor and the stepper motor.

Thanks

I would use a higher voltage pack to drive the motor then regulate it down for the Atiny. Be sure to use sufficient filtering caps - as battery state of charge goes down, internal resistance goes up and as you put a load (stepper motor) on the batteries, the drop you get will cause a reset of the Atiny if it goes down too far. There are some quite efficient switching regulators available in a TO-220 type case that are efficient replacements for the LM78xx type things (linear) that could give you better battery life. Check out the OKI-78SR-5 like THIS

paulwece:
Can I use 4 NiMH batteries that will provide 4.8 -5V roughly to power a chip that needs 5V?

The battery voltage might drop as it get discharged. I wonder how much it will affect the chip performance? I'm talking about the ATtiny85.

Thanks

No, 1.2V is the nominal voltage of a NiMH cell, when fully charged, the voltage is around 1.45V: 4 * 1.45V = 5.8V, which is 300mV higher than the ATtiny's maximum rating.

Pieter

Check out DC-DC boost converters. You can get 5V from as low as 0.9V with some, and a USB charge port to connect to for about 2 Eu.

Also look into DC-DC buck converter to convert higher V to lower with 90% or better efficiency.

PieterP:
No, 1.2V is the nominal voltage of a NiMH cell, when fully charged, the voltage is around 1.45V: 4 * 1.45V = 5.8V, which is 300mV higher than the ATtiny's maximum rating.

Pieter

So I guess powering the ATtiny at a voltage higher than its max rating would destroy it.

But what about powering the stepper motor at a voltage lower than 5V (its nominal is 5V). Do I merely get less torque or does it not work at all?

Looks like if I want to use a common power source, there is no getting around using either a boost or buck converter huh?

paulwece:
But what about powering the stepper motor at a voltage lower than 5V (its nominal is 5V). Do I merely get less torque or does it not work at all?

It will have less torque, and might skip steps, or not take any steps at all. If you lower the speed, you can prevent this.

Pieter

paulwece:
So I guess powering the ATtiny at a voltage higher than its max rating would destroy it.

But what about powering the stepper motor at a voltage lower than 5V (its nominal is 5V). Do I merely get less torque or does it not work at all?

Looks like if I want to use a common power source, there is no getting around using either a boost or buck converter huh?

At a certain point.

Less torque until the voltage is low enough that the control circuitry doesn't work and it stops entirely or starts to behave erratically. As you are outside of spec'ed operation range, you can't be sure if behavior will be the same from unit to unit, either - so i'd try to avoid this.

No, if you start with a voltage too high for the ATTiny, you could use a 5v or 3.3v linear regulator (do be aware of dropout voltage) to supply the attiny with an appropriate voltage.

You don't want to have the power supply for the tiny be the same as the supply for the servo - servos and other motors put a lot of noise onto the power rail, leading to instability. You may be able to get away with a regulator and caps, but you'd be much less likely to be okay even if you did have some magic battery that was within both the tiny's and the servo's range in expected operating conditions.

DrAzzy:
At a certain point.

Less torque until the voltage is low enough that the control circuitry doesn't work and it stops entirely or starts to behave erratically. As you are outside of spec'ed operation range, you can't be sure if behavior will be the same from unit to unit, either - so i'd try to avoid this.

No, if you start with a voltage too high for the ATTiny, you could use a 5v or 3.3v linear regulator (do be aware of dropout voltage) to supply the attiny with an appropriate voltage.

You don't want to have the power supply for the tiny be the same as the supply for the servo - servos and other motors put a lot of noise onto the power rail, leading to instability. You may be able to get away with a regulator and caps, but you'd be much less likely to be okay even if you did have some magic battery that was within both the tiny's and the servo's range in expected operating conditions.

I think it might be easier to just use a separate power source for the ATtiny85. It uses very little current, so perhaps even a button cell will last a long time. A 3V button cell like CR1632 might work right? Because the ATtiny can work as low as 1.8V as someone stated. And when you think about it, lots of real products like key fobs that uses microprocessors are powered using button cell.

paulwece:
Because the ATtiny can work as low as 1.8V as someone stated.

The ATtiny85V which is not the same as an ATtiny85.

Buck converters for max rated output 3A are end joint of finger small. A 7805 regulator is smaller and cheaper but simply wastes excess power, not so good for batteries.

Whatever you use, how will it control the motor? How many milliamp hours do the button cells have?

GoForSmoke:
Buck converters for max rated output 3A are end joint of finger small. A 7805 regulator is smaller and cheaper but simply wastes excess power, not so good for batteries.

Whatever you use, how will it control the motor? How many milliamp hours do the button cells have?

http://www.embedded.com/electronics-blogs/break-points/4429960/How-much-energy-can-you-really-get-from-a-coin-cell-

Since the ATtiny need 5V and button cells are usually 3V, shouldn't a boost converter (rather than buck) be used?

The microprocessor will control the motor so that the shaft will rotate counterclockwise for one rotation, reverse direction, and repeat. The rotating frequency is not that high, maybe 0.5 rev/sec.

The CR1623 seem to have 160ish mAh.

Since the ATtiny need 5V

NO.

Aren't you reading the replies?

What are you using for a motor driver? I have had good results running a 28byj48 using either a TB6612 or DRV8833 driver. They are pretty similar. I started out using a 'darlington array' like in the stepper motor tutorial, but it was slow, and only worked in unipolar mode.

You can use the 28byj48 in bipolar motor, by just ignoring the red 'common' wire.

This way, you can run the motor at up to 12 volts with it's own power supply. Two aaa cells will run a tiny85 just fine. Just be sure to connect the ground of the motor's power supply to the negative battery terminal of the processor's supply.

paulwece:
Since the ATtiny need 5V and button cells are usually 3V, shouldn't a boost converter (rather than buck) be used?

The microprocessor will control the motor so that the shaft will rotate counterclockwise for one rotation, reverse direction, and repeat. The rotating frequency is not that high, maybe 0.5 rev/sec.

The CR1623 seem to have 160ish mAh.

First, the controller can run at 1MHz at 2V with some margin over 1.8V where any less causes resets.

How fast or slow the motor runs, some mA must be spent keeping transistors in the motor driver open even when they don't change.

When you already have a main power source that you can tap very efficiently, why add another to watch and maintain? If it was a matter of using a wastey 74xx regulator, I could see that but it's not.

jremington:
NO.

Aren't you reading the replies?

I do read the replies carefully. Just got a little confused. I understand the ATtiny can work as low as 1.8V under certain conditions.

Now that I have a better understanding of the "grand scheme" of things, I reread all the replies again and feel it's best to use a single power source at a higher voltage for the motor, and regulate it down for the ATtiny85.

Member gpsmikey's solution:

I would use a higher voltage pack to drive the motor then regulate it down for the Atiny. Be sure to use sufficient filtering caps - as battery state of charge goes down, internal resistance goes up and as you put a load (stepper motor) on the batteries, the drop you get will cause a reset of the Atiny if it goes down too far. There are some quite efficient switching regulators available in a TO-220 type case that are efficient replacements for the LM78xx type things (linear) that could give you better battery life.

I believe this is what GoForSmoke meant by "When you already have a main power source that you can tap very efficiently, why add another to watch and maintain? "

thanks