A Digital Voice Recorder/Keyer Controller for the IC-756Pro II

by Larry Handwerger N2LH

Larry N2LH using the DVR Controller during the ARRL SS Phone Contest.
Fig. 1. Larry N2LH  using the DVR Controller during ARRL SS

This page describes the IC-756Pro II Remote DVR/Keyer Controller designed and built by Larry,N2LH, withthe following features:

  1. Four pushbutton switches (S1 through S4) for remote memory selection.

  2. A PTT / XMIT selector switch (S6).

  3. A PTT pushbutton switch (S5).

  4. An RCA jack for a foot switch (J3).

  5. A microphone input jack (J1) Note: Larry uses the HC-5 headset.

  6. A 0.47 µF blocking capacitor (C1) in series with the MIC HOT line, to keep the +5V DC off the Heil element.

Schematic of DVR/Keyer Controller. Copyright N2LH.
Figure 2. Schematic of DVR/Keyer Controller.




C1 0.47 µF 50V ceramic
J1 3mm mono jack
J3 RCA jack


1.5K 0.25W 5% metal-film


1.5K 0.25W 5% metal-film
R3 2.2K 0.25W 5% metal-film
R4 4.7K 0.25W 5% metal-film
S1, S2, S3, S4, S5  SPST non-locking pushbutton switch
S6 SPDT toggle switch (On-Off-On)
Table 1. Component List.

Construction: As will be seen from the pictures, the DVR/KeyerController is built into a Radio Shackutility box. A die-cast aluminum box is also suitable. All therequired parts should be available at your local Radio Shack store.

The 0.47 µF (4700 pF) blocking capacitor is used to block the phantom +5VDCon pin 1 of  the MIC connector. (Refer to IC-756Pro II User Manual, p.9).This capacitor was purchased via mail order from an electronics partssupplier; Radio Shack did not stock it. A higher value (0.68 to 1.0 µF) is alsousable, and may be in stock at Radio Shack.

I used a plastic utility box, as I wanted to separate ('float') themicrophone and PTT grounds;  the microphone  jack is not insulatedfrom the the box. Because of that, I used a small piece of shielding braid takenfrom RG-174U coax to put over the microphone hotand ground leads. I soldered this shieldingto the ground of the cable which plugs into into the IC-756Pro2 MIC socket. Thebraid is covered with heat-shrink tubing. I was concerned about RF getting intothe microphone input.

If a metal box is used, the microphone jack should be insulated from the boxto isolate the MIC ground.

Operation: Please refer to the IC-756ProII User Manual,  p. 73, "ExternalKeypad" for menu setting information and operating instructions.

External view of DVR/Keyer Controller.
Figure 3. Exterior view of DVR/Keyer Controller.


Internal view of DVR/Keyer Controller.
Figure 4. Interior view of DVR/Keyer Controller.

Contents copyright  2002 Larry Handwerger N2LH (including all images). All rights reserved. 
Page created by A. Farson VA7OJ/AB4OJ. Last updated 09/25/19
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