This is my first post, and I've been playing around with a Picaxe for a little while now. I no longer want to run the Picaxe from a battery unit. Now I can hook up a voltage regulator to it, but are there any extra componets that I have to add to have proper and safe power going to the Picaxe?
Proper Way For Powering A Picaxe From a Regulator
- Thread starter K-Young
- Start date
Most people use the 7805 regulator to provide stable 5V from an unregulated source (typically 9 - 15V). That regulator is a pretty forgiving one.
Good practice though:
P_diss = (V_input - 5V) * I_load
Good practice though:
- 100uF electrolytic capacitor between regulator input and ground.
- 100uF electrolytic capacitor between regulator output and ground.
- 0.1uF ceramic capacitor between Picaxe power and ground, somewhere close to the Picaxe.
- A sufficiently high-power diode in front of the regulator input to protect it against accidental reverse polarity.
P_diss = (V_input - 5V) * I_load
Thanks for the quick response. I figured the Electrolytic capacitors were required, but the ceramic cap and the diode are new to me. Sounds simple enough.
westaust55
Moderator
7805 & 78L05 regulator circuit
Welcome to the PICAXE forum.
There is a circuit using a 7805 type voltage regulator in PIACXE manual 1 (rev 6.9) page 24 that may be useful for you.
Welcome to the PICAXE forum.
There is a circuit using a 7805 type voltage regulator in PIACXE manual 1 (rev 6.9) page 24 that may be useful for you.
The capcitors are there to buffer fast changes in the current consumption where the regulator cannot react fast enough. It's good practice to place such a small ceramic capacitor close to every chip on your board so it "decouples" the high-frequency range for that chip's power supply. The larger electrolytic capacitor then buffers slower changes. (For modern, fast digital circuits - into the GHz range - this power decoupling has become a real art, with quite a few books and many papers written about it, and people are using powerful simulators to come up with the correct selection of capacitors; fortunately typical Picaxe circuits are far from such requirements and you can get away with such rules of thumb).
Many modern regulators can actually be quite sensitive and require some minimum and/or maximum capacitance to work correctly; outside that range they may start to oscillate. But the 7805 is very well-behaved in that respect, which is one reason it is still so heavily used in hobby applications.
Many modern regulators can actually be quite sensitive and require some minimum and/or maximum capacitance to work correctly; outside that range they may start to oscillate. But the 7805 is very well-behaved in that respect, which is one reason it is still so heavily used in hobby applications.
K-Young.
Read the wise advice above.
And also always get hold of the Data Sheet for the regulator you wish to use.
There are zillions of different ones on the market.
Many look physically the same but their 'pinout' (i.e. what the little legs do) are often different.
May I just suggest the main parameters you should look at on the Data Sheet.
1. Obviously the Voltage Out.
And, if you use an adjustable type then check the equation to work out resistor values.
2. The Maximum Voltage INput.
Do not exceed it.
3. The voltage 'dropout'.
A regulator needs a bit of voltage 'headroom' to give you your 5V.
With a linear regulator like 7805 and many others, you need to supply it with a voltage that is higher than your desired output voltage.
How much higher? basically it will be Vout + Vdropout minimum.
Some regulators are called 'Low Dropout' or LDO. They don't need so much voltage headroom and are better with batteries (your batteries will last longer).
4. Quisecent Current.
i.e. basically, how much power the regulator uses to give you your desired voltage.
Can be important for battery powered devices.
The 'old faithfull' 7805 is a lovely, quaint, cheap, reliable regulator.
It is so old that archeaologists regularly find them in ancient rock strata.
It has a dropout voltage of 2V so you need to give it with >=7V to make it happy.
So, being powered by 4xAA wouldn't be good.
Anyway, have a look into the Data sheets.
For low power battery stuff look into LM2936 an LP2950 types.
But honestly, there are loads and if everyone posts their 'favourite' regulators it'll make you cross-eyed
We'll move onto power calcs if things get hot.
Read the wise advice above.
And also always get hold of the Data Sheet for the regulator you wish to use.
There are zillions of different ones on the market.
Many look physically the same but their 'pinout' (i.e. what the little legs do) are often different.
May I just suggest the main parameters you should look at on the Data Sheet.
1. Obviously the Voltage Out.
And, if you use an adjustable type then check the equation to work out resistor values.
2. The Maximum Voltage INput.
Do not exceed it.
3. The voltage 'dropout'.
A regulator needs a bit of voltage 'headroom' to give you your 5V.
With a linear regulator like 7805 and many others, you need to supply it with a voltage that is higher than your desired output voltage.
How much higher? basically it will be Vout + Vdropout minimum.
Some regulators are called 'Low Dropout' or LDO. They don't need so much voltage headroom and are better with batteries (your batteries will last longer).
4. Quisecent Current.
i.e. basically, how much power the regulator uses to give you your desired voltage.
Can be important for battery powered devices.
The 'old faithfull' 7805 is a lovely, quaint, cheap, reliable regulator.
It is so old that archeaologists regularly find them in ancient rock strata.
It has a dropout voltage of 2V so you need to give it with >=7V to make it happy.
So, being powered by 4xAA wouldn't be good.
Anyway, have a look into the Data sheets.
For low power battery stuff look into LM2936 an LP2950 types.
But honestly, there are loads and if everyone posts their 'favourite' regulators it'll make you cross-eyed
We'll move onto power calcs if things get hot.