$50 Robot query

[robaker]

What is the appropriate voltage for the circuit ?
In case 1: Its written to provide 6V ( both for 2 servos and the circuit)
while in case 2 : 4.8 V for servos and 9V for circuit.
Thus, why 9V in case 2 why not 6V ?
 

[Soeren]

Hi,

Thus, why 9V in case 2 why not 6V ?

Because a PP3 battery is a small package and since you need 5V, you have to regulate it down.
A 9V battery goes down to 5.4V when flat.

[robaker]

if 5V is needed that could be obtained by 6V battery/supply as done in case 1 with 5xAA NiMH. plz if you could explain such concepts of voltages as for beginners may be beneficial.
Thank you for replying.

[cyberfish]

It's difficult to get 5V from a 6V battery because normal regulators (LM7805) require about 2V dropout (to provide a constant 5V, input needs to be above 7V).

To get 5V from 6V you will need a low-dropout regulator (LDO), which has weird output capacitor requirements to be stable, or a switching regulator, which also require external components, and are quite a bit more expensive.

[Soeren]

Hi,

if 5V is needed that could be obtained by 6V battery/supply as done in case 1 with 5xAA NiMH. plz if you could explain such concepts of voltages as for beginners may be beneficial.

5 NiMH cells are 5*~1.45V = ~7.25V when fresh from a charger and considered flat at 4.5V to 5.5V, depending on the current draw.
7.25 is way too much for the controller so you need to add (LDO) regulator.