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25 septembrie 2014

LiIon charger with LM317 and Cutoff circuit - Part I

Very often I need to charge one or two series LiIon cell for my experiments.
I do have a sophisticated battery charger and analyzer but I don't want to use it every time.
I need something simple yet safe.
There fore I came to a nice shematics here.



It is a very simple schematics using just one LM317 and two NPN transistors.
I made some modifications.
The most important is R7 which is 6 Ohm for a 210 mA current.

Despite the urban myths, the Li based batteries are very safe at charging if you respect two rules:
1. No more than 4.2 V per cell
2. No more than 1.5 C (thats 1.5 x Nominal capacity in A) charging current.

The main advantage is that at the end of charging, when the battery has the desired voltage - in our case, 4.2 V/Cell, the charging current drops to zero. The bonus is that the LED lights during the charging phase.

Yes, I know, there is CAD but I like the old fashion way to make a PCB. By hand with a fine marker...

Here are some pictures....













I plan to put this with a 12V/2A SMPS into a small box.

09 septembrie 2014

Kantronics KAM Plus

So...
I found on my junk box a Kantronics Kam Plus modem. It stayed there about 2 years untill I found (yes, in my other junkbox) a 25 to 9 pin COM adapter...
I connected to a terminal and nothing happened, just garbage on my screen so I search on internet  and came to this reset procedure:

1)  Open the case
2)  With modem power off, install Reset Jumper, K6 (near the largest IC), on the two posts.  ( no need to touch the battery).
3)  Using terminal program (WinPack or others) with baud rate set to 1200, power on the modem.
Modem should respond with :

CHECKSUM OK
....RAM OK
128K BYTES
REPLACE TEST JUMPER

4) Power off the modem; return jumper K6 to one pin only.

5)  Power up the modem;  Watch for: 
PRESS (*) TO SET BAUD RATE*   (You must do this within 2 seconds).

ENTER YOUR CALLSIGN=>
ENTER YOUR CALLSIGN=> yo3hjv
yo3hjv
KANTRONICS ALL MODE COMMUNICATOR PLUS Version 8.2P
(C) COPYRIGHT 1988-1997 BY KANTRONICS INC.  ALL RIGHTS RESERVED.
DUPLICATION PROHIBITED WITHOUT PERMISSION OF KANTRONICS.
cmd:

You should now be in NEW USER mode. 

6)   Check your call sign by typing    MYCALL

8)  To change from NEWUSER mode to TERMINAL mode type    INTERFACE  TERMINAL

cmd:in terminal
in terminal
INTFACE was NEWUSER
cmd:

9)  To change from 1200 baud (because Airmail doesn't go that slow)  type in ABAUD  0 
cmd:abaud 0
abaud 0
ABAUD was 1200
cmd:

Now, everything is ok , awaiting a proper radio and setup to test. Unfortunately, only CW and RTTY seems to be appropiate in these days since PACTOR, AMTOR and other modes like that ceased in favor of PSK.
Maybe this nice modem will find it's place as a APRS digipeater, who knows!



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