Modification of the Montreal Doppler II hardware
to utilize features of the alternate firmware

Important notice - please read:

These modifications apply only to a Montreal Doppler II unit that has been fitted with the alternate firmware.  This firmware was based on code originally written by Jacques for the Montreal Doppler II.

Many new features have been added and most of the code has been extensively rewritten without Jacques' direct involvement, so he cannot be reasonably requested to provide support:  Please use the contact information at the bottom of this page if you have any questions.

Purpose of modifications:

The alternate firmware allows these additional features to be used on the Montreal Doppler II unit:

Audio level metering:

Synchronous Serial Compass Rose data output:

The Montreal Doppler III has an synchronous serial output (SPI-type) that feeds a 36 LED compass rose display that shows the bearing.  This firmware also provides a compatible serial output to such a display.  This data stream is compatible with the original display supplied with the Doppler III unit as well as the Alternate firmware for the Compass Rose display.

Note:  It is presently unknown if just the compass rose display board is available.  The schematic/details of this display board may be found on the Montreal Doppler III page.  For information on the alternate firmware for this display, use the contact information at the bottom of this page.

Clock output for an outboard switched-capacitor filter:

A "Roanoake-type" 8-capacitor switched-capacitor filter may be added to the Doppler II:  The new firmware outputs a clock that may be used to directly drive an Add-on Switched-capacitor filter.

Schematic of audio level metering modification for the Montreal Doppler II
Figure 1:  Schematic diagram of the added audio level detector.  The ground is tied to any convenient ground on the circuit board.

Audio level meter modifications:

Some minor modification of the Doppler II circuit board must be done in order to connect the audio level detector input.  These modifications are as follows and are noted in the diagram:

After this is done, use an ohmmeter to verify that there is no low-resistance continuity between the +5 volt supply and pin 4 of IC3.  Also verify that there is continuity between pin 5 of IC3 and the newly-jumpered leg of R7 and verify that both of these do have continuity to the +5 volt supply bus.  Note:  There may be some high resistance readings between pin 4 of IC3 and the +5 volt supply, but these may be due to the input circuit of IC3 itself.  If the trace wasn't properly severed, the reading will be in low-ohms range (e.g. less than 10 ohms.)  Do not use an analog ohmmeter set to the "1 ohm" or "10 ohm" scale for this sort of measurement!  Do not omit the 470 ohm resistor:  Without it, the modification may not be reliably detected.
Figure 2:  This display shows the detected status of the modifications for audio level metering ("LVL Mtr"), the data output to the compass rose  ("ROSE") and the clock output for the added switched capacitor filter ("SCF")

The output of the peaking filter (IC2, pins 6 and 7) is connected as an envelope detector as depicted in the schematic in Figure 1.  The DC output of this detector is connected to pin 4 of IC3.  For this modification, pin 4 must be isolated from the +5V power supply bus and a jumper added to reroute the +5V bus as described above.

Once this modification is installed, the firmware must be instructed to detect these modifications.  This may be done one of two ways:

With these buttons pressed, the startup sequence will include a display showing the detected status of the modifications, as shown Figure 2.
Figure 3:  This display shows the display without detected audio level hardware.  Note the "square with line" icons around the quality reading on the left side of the screen in leiu of the "audio level" icons.

If you are successful, the detected status of the audio level metering and the SPI interface for the compass rose will be displayed.  If the displayed status is "1" (as shown in Figure 2) that indicates that the firmware has detected that the modifications have been done, and a "0" of the circuit board traces appear to be in their original configuration.  Another indication that this modification may be successful is that "N/A" will no longer appear under the "AFGATE" parameter in the last menu.

Note:  This modification is detected by checking to see if pin 4 of IC3 is tied to the +5 volt bus.  It cannot detect the actual presence of the added circuitry - only that pin 4 has been isolated.

Synchronous serial output modifications for the compass rose:

This modification is straightforward:

Once this modification is complete, the procedure for forcing detection (e.g. holding buttons down while powering up, as mentioned above) is done.  The firmware simply detects the presence of this modification by checking to see that neither pin 23 or 24 is grounded  It cannot detect the actual presence of a compass rose or any other hardware.  Another indication that this modification may be successful is that "N/A" will no longer appear under the "ROSE" parameter in the last menu.

Switched capacitor filter clock output:

This is another straightforward modification:

This modification simply detects whether or not pins 9 and 10 of IC3 are still connected to each other:  It cannot detect the actual presence of the switched capacitor filter or any other hardware.

Adaptive filter modification (firmware version 7A and newer):

In firmware versions 7A and newer, an "Adaptive filter" feature is available.  To use this, one must already have done the "Audio Level Meter modification and have a switched-capacitor filter installed.  This modification involves isolating pin 5 from the +5 volt bus (a simple matter of cutting the trace between pins 4 and 5 if you have already done the "Audio Level Meter" modification - see above for more information) and using this signal to operate an analog gate (such as a 4066) by "short out" the damping control.

What if you do not have the switched-capacitor filter installed?  As long as you have the "audio level metering" installed, you can get most of the benefit if the "Average Clear" function is used.  The added switched-capacitor filter provides additional filtering when needed (that is, when the "damping" or "Q" control is turned up) but while this improves performance in the presence of weak/noisy/heavily-modulated signals, it greatly slows the response to brief transmissions.  The adaptive filtering (described here) causes the filter to automatically switch back to a "fast" mode when the currently-monitored signal goes away as well as help "pre-load" the switched-capacitor filter with some of the new signal when it appears, before switching to the "slow" mode, as set with the "damping" control.

Schematics/additional details of this modification will be added shortly - send an email to the address below if you want more information.


Do you have any questions on this or other DF-related topics?  Go here.

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This page updated on 20110124

Since 1/2011: