Re: CW Offset does NOT work on Raduino_v1.14.1 for BITX40
|
Admittedly, my memory's not what it used to be, but I don't remember anyone blowing an Nano I/O pin. I'm sure there have been some who somehow connected 12V directly to an input pin but, to me, that's a $3 lesson that they needed to pay.?
Jack, W8TEE
From: Jerry Gaffke via Groups.Io <jgaffke@...>
To: [email protected]
Sent: Wednesday, June 14, 2017 7:10 PM
Subject: Re: [BITX20] CW Offset does NOT work on Raduino_v1.14.1 for BITX40
The reason to go with the output of the 78L05 was because it swings between 0 and 5v, which is the range acceptable to the Nano. But looks like we want two resistors to do that properly. Perhaps the 10k series resistor ?from 78L05 to the Nano is not absolutely needed, but we've seen enough blown Nano IO pins here that I would definitely include it in case the 12v TX line goes high but the Raduino is not powered up for some reason. Might be more straightforward to instead sense the 12v TX line using a resistive divider of 20k and 10k in series,? with 12v TX into the top of the 20k, bottom of the 10k to ground. The join between the 20k and 10k goes to the Nano's A0 input. The 78L05 is not involved. So the Nano sees 12v * 10k/(20k+10k) = 4v when TX is at 12v, otherwise 0v. Your choice, either this or the two 10k's on the 78L05, either should work just fine. ? Jerry On Wed, Jun 14, 2017 at 03:53 pm, Jerry Gaffke wrote:
Adding a 10k load to the 78L05 will not affect bias to the IRF510 gate.
The 78L05 can supply between 0 and 100ma while maintaining a constant 5v at the output.
That 10k resistor will draw an extra ?5v/10k = 0.5ma.
Jerry, KE7ER
?
|
