Here are a few comments on using the PK-2 chip with the Norcal 20 or the Red Hot Radio: 1) The PK-2 can be used without a pot (VR) speed control but you should let pin 2 "float" (disconnect it from ground in the NC-20 or other applications). Originally, the Tick documentation that I have had pin 2 open, now the in Norcal 20 it's connected to ground. I will have future versions of the PK-2 check for a grounded connection on pin 2 and automatically go to paddle speed setting instead of the awkward 39 WPM speed you'll see with the present version. 2) C6 is necessary for pot (VR) speed control. The internal A/D converter is not available on pin 2 of the PK-2 chip so an alternate method is used to sense the pot (VR) position. The series 1 k resistor (R3) is also needed to prevent shorting pin 2 to ground when the output is high. 3) Note, 10/2/99, this item has been changed in the latest PK-2 version The sidetone of the PK-2 is going to have more "thump" than the Tick when used in the NC-20. This is due to the fact that the sidetone pin is NOT "tri-stated" when the tone output is off. I will probably make this selectable in a future version of the PK-2. Also, the PK-2 sidetone frequency is higher (roughly 750 hz) versus the Tick (about 600 hz). The reason for my not floating the sidetone pin is that a piezo sounder connected to a floated output pin will eventually drift into the active digital region and increase the standby current of the keyer chip by a large amount. 4) Here is a battery backup mod for the Tick or PK-2 used in an NC-20 (this was originally sent to the qrp-l email list): I did a battery backup mod for my own PK-2 keyer chip and the NC20 which has worked fine for the last couple of months. I used a pair of AA cells but a lithium cell should work fine. A trace on the bottom side of the board will have to be cut. Components required: 2 1n34 diodes (from Radio Shack), 1 .22 uf ceramic cap. (you could substitute 1n5817-19 or other schottky diodes but they are harder to find and more expensive - I would avoid using regular switching or power diodes since they have a larger forward voltage drop). 1) Cut the trace on the bottom of the board from pin 1 of U9 to C91 (a wide diagonal trace). 2) Solder the cathode (banded end) of one of the diodes to pin 1 of U9. Solder the anode of the same diode to the C91 connection (a series diode is used to make the connection to the 5 Volt supply). 3) Solder the cathode (banded end) of the other diode to pin 1 of U9. Solder the anode to the positive lead of the 3 volt battery holder (a series diode is used to make the connection to the battery). 4) Solder the negative lead of the 3 volt battery holder to ground. 5) Solder the .22 uf cap from pin 1 to pin 8 of U9 (this decouples the power supply of the keyer chip). 6) Power up the NC20 and install the battery - the keyer chip should now retain any settings made. The idea is to use the diodes to isolate the battery from the 5V supply. When the power to the NC20 is turned off, the voltage on pin 1 of the keyer chip will decay until it reaches the battery voltage (minus a single diode drop). The battery voltage will allow the keyer chip to retain any memory or other settings. However when the NC20 is powered up, the power for the keyer will be drawn from the +5V supply. The multilayer ceramic cap is needed to filter any spikes which may occur when switching back and forth from the battery to the normal 5 volt supply. Here is my attempt at an ascii schematic: 1n34 ------|>|------ (cathode) + | | ------- | --- 3v | ------- battery | --- | - | | | | gnd | | | | .22 uf +5V 1n34 | _____________| |____________ |------|>|--- | | | | | | | | | _______________ | | cut | | | | | | |___X_______| ______|___|_____|1(pwr) (gnd)8|______| | X | | | | U9 - keyer | _|_ | | ___ c91 | | | gnd Best Regards, Chuck, WB9KZY Jackson Harbor Press jacksonharbor@worldnet.att.net