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@ -1,18 +1,5 @@
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Denon PMA-770 (and others) Arduino Control
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# About
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This project ultimately seeks to be a "logic control" modification for a
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Denon PMA-770; allowing one to do things like change inputs, volume,
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balance, and tone using a remote control.
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But that's a long ways down the road; so right now it's goal is to drive
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relays and a display to replace the source input switches and input
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display. I am designing it around the aforementioned Denon; but it can
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obviously work for other units with some modification.
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Schematics and pictures up later.
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# History
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```
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@ -21,5 +8,114 @@ Schematics and pictures up later.
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29-Dec-2019: Version 0.1.1 - Added preliminary IR remote support
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30-Dec-2019: Version 0.1.2 - Controls ShiftReset and OutputEnable on 595 to prevent random start-up state.
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30-Dec-2019: Version 0.1.3 - Removed ShiftReset function. Replaced with reset circuit onboard.
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01-Jan-2020: Added license, media, and proper README.
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````
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# About
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The Denon PMA-770 is a high-end integrated amplfier from the early 80's capable of the usual 100 watts into
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8 ohms; and somewhere in the neighborhood of 120 to 140 in to a 4 ohm load. It's a DC coupled amplifier of
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"Direct-A" topology. It's got 3 pairs of output transistors, no capacitors in the audio path, and it sounds
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outstanding.
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But it's also got this seriously stupid way of working the input switching that has not only caused failure
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of most of the inputs; but is silly enough I don't want to bother trying to replace the switches to keep the
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original method in tact. In order for the audio to make it in to the amplifier, it relies on connecting through
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the "normally closed" contact on the switch "in front" of it. Well the "normally closed" contact has decided it
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no longer wants to close and the entirely sealed design has prevented cleaning agents to make it in.
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To add to the stupidity; this unit features a simple segemented LCD display to display the name of the input.
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This was a probably a pretty big ordeal in an era where even a single LED lighting up over the name was an
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entirely new idea. This display is non-standard and relies on even more contacts in each input switch to throw
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pins to AC. Disabling the input switches would disable this display; but the 128x32 OLED looks like it will fit
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in the phsical space the existing one does.
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Taking that in to account, I decided to build a relay board driven by an Arduino that would also drive the
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display. It also lets me do crazy things like add input selection by remote control...something you weren't
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getting back in 1981. Additional modifications like motorized pots for volume could further extend the
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remote control function.
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# Hardware
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The basic idea is parallel the actuator contacts of 5 DPDT (or DPST) relays and flip them on one at a time (two
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for phono).
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[*Click for full resolution.*][/images/schematic.png]
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Data is shifted in to a 74HC595 and it's parallel outputs are used to control a ULN2803(or 2003) darlington array to
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in turn drive a relay. The output of the 74HC595 is controlled by the microcontroller and an RC circuit on the reset
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line prevent suprious relays from firing. Every effort has been taken to ensure only one relay will be fired at a time
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to prevent damage to other audio components. The 2803/2003 arrays include built in snubber diodes for inductive kick-
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back protection. If you should deviate from this schematic and use discreet diodes, you must add these diodes to your
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circuit or you will damage the transistors, shift register, and/or Adruino.
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The switch matrix consists of a simple resistor based analog method that merely throws different amounts of voltage thru
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resistors. While this allows us to read all of our switches using just one line, it can cause problems should you want to
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trigger two buttons. On the PMA-770 this is fine as the original bank of switches are mechanically linked to allow only
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one to be active at a time. It is possible to read dual inputs as long as the parallel resistance doesn't cause a value
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close to any indvidual switch. I have included a small utility in the /utilities folder that will display the current
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ADC integer value to the LCD display. It can be used for just figuring out which resistors to use, or to check behavior
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of paralelled resistors (two button press scenario). Using one line for the switch matrix is not set in stone and may
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change depending on needs and availability of pins going forward.
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The Phono-1 and Phono-2 inputs are the only time the unit will ever fire two relays. This is because on the original
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unit itself; both of these inputs route the phono-stage preamp to the main amplifier while routing the cartridge input to
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the phono-stage.
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An 1838 IR sensor is used for remote control function. An additional utility may be written to help with this going forward
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but it's possible I may wind up writing a routine for "self-programming".
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Currently I am using an I2C 1602 display just for development purposes. This will be replaced with a 128x32 I2C OLED display
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in the future. This display is just a little larger than the display in the Denon; so it shouldn't be any issue to mount it
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and format everything to appear in the actual visible space. It is not shown on the schematic; however it is just connected
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to 5V, GND, SDA, and SCL lines.
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In the future I will be adding some kind of NVRam storage. This will facilitate actually storing configuration options, remote
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programming codes, and to store the last-used input. I may also use this to store graphic data for the OLED display to
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emulate the original segmented font display of the Denon.
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# Media
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[*Prototype & Development Build*
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This is a previous revision of the hardware before the power-on reset circuit was added to the 74HC595. The parallel data is
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represented by the standard arrangement of LEDs with current-limiting resistors. This is literally all that's required during
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development since I'm already very familiar with the 2803 as a driver.
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I'm horrible at making videos in general...but I still made an attempt to show things off.
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<!-- blank line -->
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<figure class="video_container">
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<iframe src="https://www.youtube.com/embed/I_sLnnsZ7Qg" frameborder="0" allowfullscreen="true"> </iframe>
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</figure>
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<!-- blank line -->
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<!-- blank line -->
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<figure class="video_container">
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<iframe src="https://www.youtube.com/embed/I30OaMii4l4" frameborder="0" allowfullscreen="true"> </iframe>
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</figure>
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<!-- blank line -->
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# License
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Copyright 2020 Jay Moore
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Redistribution and use in source and binary forms, with or without modification, are permitted
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provided that the following conditions are met:
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1. Redistributions of source code must retain the above copyright notice, this
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list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
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and the following disclaimer in the documentation and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
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WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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THE POSSIBILITY OF SUCH DAMAGE.
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