Society of Robots - Robot Forum

Ah! You dead bug solder a chip, and can get down in size. None of the commercial units I found were anywhere near as small,

then i highly recommend checking out dave theunissons commercial products:

http://www.micronradiocontrol.co.uk/rx_dt.html

there are other similar sub-nano rx available from similar companies but his are most popular. having had considerble experience with those ook units i assure you, even before attaching controllers to make them work, they are much bigger. basically legacy designs from early car/garage keyfobs and have been replaced with modern 2.4ghz transceiver modules which are cheaper and outperform.

in any case imo off-the-shelf rc rx is by far the cheapest and easiest path for wireless control. bare rf modules and ir circuits can be made to work but require considerable expertise and experience.

i should also mention the sparkfun ook device linked is the tx which op mentioned was not size constrained. the rx is much bigger. and niether are functional out of the box. little more than uhf front ends really. as mentioned a computer is required at each end to decode any control signals.

the rc units are smaller, cheaper, and ready go regarding control of servos, lights, or motors.

Circuits draw current. Power supplies do not "push" current. A power source (wall wart, battery, whatever) will only be able to supply a certain amount of current before overloading, so circuits that draw more than the rated current will see problems.
For wall warts, you may have a fuse or PTC blow if you draw too much.
For batteries, you will see the voltage sag, and the battery potentially overheat.
For well designed power supplies, you will see the voltage drop until the circuit only draws the design limited current (this may be very close to 0 Volts for a short)

Separately, voltage measures how hard/hot you're driving a circuit. While a specific circuit will likely be designed for a specific voltage, smaller variations will often work fine. Larger variations may either cause lower/higher than expected performance (motors, heaters, etc) or destruction of components not designed for the voltage range (capacitors, etc.) Also, a higher voltage will cause a resistive circuit to draw more current. A 100 Ohm circuit at 3 Volts will draw (3/100) == 30 mA. At 6 Volts, it will draw (6/100) == 60 mA. Because power is the square of current (also the square of voltage,) the 6 Volt version will dissipate 4x the power, and likely overheat whatever was designed for 3 Volts.

So, battery, runtime. If the battery provides the appropriate voltage for a circuit, then larger capacity (Ah or Wh) will mean longer run times, all else being equal. Some batteries also have significant self-discharge, that may need to be factored in if you're talking about weeks or months of runtime.

If the power source provides a voltage that is not suitable for the circuit, then you need to regulate the voltage. For a 12V battery driving a 1.8V LED, you will need to drop at least 10V. The easiest way to do this is to look up the current usage of the LED (10 mA, say) and then calculate the appropriate resistance to drop 10V at 10 mA (U = I * R means R = U / I means R = 10V / 100 mA == 100 Ohms.) Now, 10V times 100 mA equals 1 Watt of power, so you will need a fatter than normal resistor for this to not burn up. Normal resistors are rated for 1/4W usually, or even 1/8W for smaller components.

If the voltage source will vary, or the load will vary, the resistor will need to vary based on the input voltage. If a battery starts out at 14V, and drops to 11V over discharge, you will need to drop between 12V and 9V. The easiest way to do this is with a linear voltage regulator. The voltage regulator will keep a set output voltage, and adjust its resistance to "drop" the rest of the voltage it sees, based on the current drawn. An adjustable linear regulator like a LM350 can easily be set to output 1.8V over a wide range of input voltages.

However, the resistor, and linear regulator, routes, are very inefficient. The fact that you get a lot of heat should tell you that! For a 1.8V LED running from a 14V battery, 85% or so of the energy will be wasted heating up your resistor/regulator, meaning you have a 15% efficiency. That's not good for runtime.

Thus, for a case like this, you typically want a switching buck regulator (DC DC converter.) These circuits use inductors, capacitors, and switches to generate one voltage from another, with much less loss -- 90% is typical, > 98% is achievable in some sophisticated designs. Thus, for the best runtime, you want a battery with a high charge capacity (Wh or Ah) and a voltage regulator with high efficiency.

If you only need 1 channel, could you use light?

i generally get the concept of Amp hour but lets say you have a plug in AC to DC adapter, one supplies 100 ma while the other supplies 210 ma what is the difference in term usage
-does it mean the 210 ma has more available current for the circuit?

also when you measure the amperage of a battery using a mult-imeter, what does the values indicate?
-the amount of current that will flow through the circuit, right?