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That 7805 regulator is designed to still work when very hot, hot enough to sizzle spit.
However, mine gets warm, but not uncomfortably hot to touch.

This may be due to everybody buying the Nano clone that is $0.10 cheaper.
The manufacturers are constantly looking for cheaper parts to shave off another penny here and there.
We have had cases where the Nano clone was pulling far more than it should, and thus?
heating up both the regulator and the Nano.?
Is your Nano hot?
If so, replace it with a new Nano for $2.30


Mike said:
>??Put a 1N4002 Diode and 47 ohm 1W in series to the regulator and add a bypass electrolytic to ground.

Good idea, though not terribly specific.
Diode is there to save your Nano when you inevitably wire up your power supply backwards?some dark night
(and the shunt reverse diode protection scheme with no fuse described in the HFSignals notes fails to protect).
So add that into the wire that carries 12v from the main board to the raduino, alternately just
lift pin 1 of the 7805 regulator and put it there.? The cathode bar marking should be on the regulator side of the diode.
The 47 ohm resistor goes in series with that diode, doesn't matter which side of the diode.

Voltage drop across that resistor should be 4 volts or less, since the raduino will be drawing
a current of around:? ? 4v / 47ohms? =? 0.085 Amps.
If that voltage drop is 6v or more, then the LM7805 will go out of regulation and the Raduino
will be powered from less than 5v.
The idea is that the resistor dissipates the power associated with that 4v drop, and the LM7805
only needs to dissipate the additional 3v drop to bring the 12v supply down to 5v.

Another option is to just put a heat sink on the LM7805 tab, and forget the resistor.

All sorts of ideas in the forum about bypass caps for the Raduino.
The LM7805 datasheet recommends a 0,33uF (or somewhat bigger) cap at the 12v input pin to ground,
without that cap it could oscillate if that 12v wire feeding it is too long.?
No cases of this have been reported, though of course few have a scope to see it,
and those that do probably knew to add a bypass cap there.
I'd put a roughly 0.33uF cap? from LM7805 pin 1 to ground (the 12v input pin),
and then put a 47uF cap in parallel with that first cap.
To be thorough, add more such caps where 12v goes into the Bitx40 main board.
In addition to making the LM7805 behave, those caps could reduce any tuning clicks you hear in the Bitx40.

Jerry