Sunday, November 18, 2018

Adding Sound to the Junkyard Entertainment Unit

Our DVD player finally has a voice

Over the past month or so, I've been playing with a DVD player that I had rescued from my local salvage yard with the idea of preparing it for a new life in my home.

While I can easily get the DVD player to start up and play movies, the DVD player was reliant on the vehicle's radio for sound, so the movies the DVD player showed were definitely of the silent variety.

While it would be fairly simply to hook up an audio amplifier to the audio outputs of the DVD player and connect a couple of wired speakers to the amplifier, I wanted to add a bit of a twist to this project  and make the audio from the DVD player wireless.

The obvious choice would have been to hook the DVD player up to a Bluetooth based connection, but I really wanted to keep the cost of the project down to a minimum.  With that criteria, I ended up settling for a much more older, but still a very robust technology - Infrared.

Before Bluetooth became the norm, the vast majority of wireless audio headphones used infrared as the means of transmitting audio signals. While they did work well, they did suffer from the drawback that the infrared transmitter and receiver needed to be in direct line of sight of each other in order to work, something that is not an issue with today's Bluetooth devices.

The good news though, is that transmitting infrared audio is fairly simple, requiring a relatively few parts to construct. A quick look on eBay turned up several infrared transmitter and receiver kits for only a few dollars. A quick click on the Buy Now button and I had 2 kits heading my way.

Infrared receiver parts

After a few weeks, the kits arrived.

Now one thing to note - that old saying "You get what you pay for" is still true. While I did get the kits in good shape and came with all the parts there was one thing that was missing - Instructions.

Now to the kit manufacture's credit, the printed circuit boards were very well marked.

Printed circuit board is well marked
Electrolytic capacitor

So the advice I would offer is this; if you a newbie to the world of electronics, this may pose to be a bit of a challenge for you, but if you have assembled a few kits before, the lack of instructions shouldn't be too much of a problem, just follow the diagram on the printed circuit board.

Installing the Electrolytic capacitor

I started assembling the kit with the most complex part first - the receiver. I started the assembly by first installing the electrolytic capacitors. For those that aren't familiar with these types of capacitors, they need to be installed in the correct polarity on the circuit board. On the capacitor itself, the negative lead should be marked on the side of the capacitor, while the location for the negative lead on the board should be also marked. So as long as you install the negative wire in the negative hole on the board, things will be fine.   Once the capacitors are installed, just solder them into place.

Next I installed the socket for the amplifier chip (don't install the chip itself onto the board) .

Electrolytic capacitor

Looking at the socket, there should be a small notch in one end of the socket itself - this notch should match a notch marked on the circuit board location for the socket. Make sure that the socket is seated into the board with the notch markings matching and solder the socket into place.

Marking for ceramic capacitor
Ceramic capacitor

With the socket in place we then installed the ceramic capacitors onto the circuit board. While these capacitors are not sensitive to circuit polarity, they can be a bit hard to understand what value they have since they typically are stamped with a 3 digit code. Once again, the circuit board held the clue. Insert the capacitor that has the same value as the one stamped on the board and solder them in place.

Board build in progress

With the capacitors installed, the next step is to install the resistors. As before, just insert the appropriate resistor into the correct spot on the board and solder them in place.

Marking for LED
Diagram on how to keep LED install correct

Finally we need to install the red LED and the infrared receiver LED.  There is a bit of a trick for LED's. On the circuit board, there is a symbol for the LED on the board for the red LED and a negative and positive terminal for the receiver. In cases like that, I tend to have a bit of a hard time knowing which side is which on a LED. In those cases I find drawing a cheat sheet quite helpful. (Oh, by the way, the short lead of an LED is the negative connection). Install the LED's in the right polarity on the board and solder them into place.

To finish up the board, I just soldered in the connectors for the speakers and the power, insert the amplifier chip into the socket (make sure that the notch on the chip aligns with the notch on the socket) and the receiver board is done.

The completed receiver

The assembling of the transmitter board is very similar, albeit with less parts. Assembly followed the exact same process that I followed for the receiver.

Infrared transmitter parts
Capacitors installed
Capacitors installed
Transistor installed
Transmitter almost complete

With the infrared transmitter and receiver all wired up, it's now time to try them out on the DVD player.
Completed infrared transmitter and receiver
DVD player and power supply

While waiting for the kits to arrive I had gone out and bought a 12 volt power supply and a power connector to hook up to the DVD player.

Luckily the Infrared transmitter also ran on 12 volts, so hooking it up to power was a simple matter of soldering it in with the power connection for the DVD player.

Hooking up the power for the transmitter

The audio input for the transmitter was a standard small head phone jack. For testing purposes I soldered the left side audio inputs of the DVD player to a similar sized headphone plug and plugged it into the headphone jack of the transmitter.

Smoke testing the transmitter

With everything all hooked up, it was time for a quick smoke test. Connecting the power to the DVD player, the red LED on the transmitter lit up with no smoke in sight - so far so good.

Receiver connected to speaker and power

With the transmitter hooked up, I then hooked up the receiver. Hook up was a simple matter of connecting the receiver to a small speaker and powering it up with a 9 volt battery.

Finally all I had to do make sure that the infrared LED's on the transmitter and receiver were pointing to each other, I then put a DVD into the player and sat back and watched the show.

How did it turn out?

Not too bad. It transmitted the audio over a fair distance (about 10 feet) and the sound quality was pretty decent, despite the fact that I was was using an almost comically small speaker.  Definitely promising enough to continue on with the project.

The next step is to now figure out how to enclose everything in a nice "home appropriate" enclosure - Stay tuned!

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