May 20, 2014

Day & Night Sampler - a raspberry pi mpd mini boombox Part 5: Hardware Configuration

See Part 4, Starting the Boombox Automatically

In this section we'll discuss connecting the VFD, the IR remote receiver, the amp and testing with a power supply.

Hook up the raspberry pi to the VFD wires according to the following diagram:

NOTE: The attached cable on the VFD I purchased routed +5V to a Yellow wire and GND  to a GREEN wire, instead of the more common Red for +5V and Black for GND.

UPDATE March 11, 2015: Tim had a question on how the audio was fed to the amp. A USB Sound Card/dongle is attached to the Pi. A 3.5mm audio cable is plugged into the USB Sound dongle. On the other end of the cable (red arrow in picture), the cable is stripped into separate right/left/ground wires and attached to the 3.7W amplifier.


 From the VFD datasheet, I could not tell if the display was 3.3V signal-level (TTL) tolerant. So, I used a level shifter to change the output of the Rpi SPI signals from 3.3V to 5V as shown in the above diagram. 

Wall power, at +5V, is being fed directly to the board shown above. The VFD takes its +5V and GND from this board, not the Rpi. GND from the Rpi is tied to the board shown above, to supply a common GND.

To connect the IR receiver, here's a diagram from adafruit learning system:



Above is a diagram of the rpi pin connections. NOTE: I used pin #23 for the lirc_rpi (IR) input pin. If you follow Dr. Monk's tutorial, he used pin #18. This can be changed in /etc/modules.



To set up the audio output, attach a 3.5mm headphone extension cable to the USB sound dongle and the other end to some speakers.

You might be able to run the raspberry pi with the VFD attached from a computer USB port. However, it's safest to power the pi from a powered USB hub capable of 2 Amps output.

Power the raspberry pi up and wait a minute or two. If all went well, you should hear sound through your speakers and, shortly after that, the currently playing song or stream will show up on your VFD.

If things aren't going well, you have some troubleshooting to do. Most often, there's a problem with a connection: jumper wires are loose or in the wrong header, for example. So, check your connections first. After checking out possible hardware issues and eliminating them, and you still have a problem, you may have something slightly different in your software setup than what I've documented here, or something has changed, say in the Debian image you're using.





4 comments:

  1. In your list of materials you listed a 3.7w amp. On this page you said you just connected a 3.5mm lead to some speakers. Did you not use the amp? If you did I was hoping I could see a diagram connecting the amp to the raspberry pi.

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    Replies
    1. Hi Tim- I have added a picture to show how the audio was attached on page 5, Hardware Configuration.

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    2. So are you powering the amp from the breadboard connected to the wall power supply? Can I use the 5v pin on the raspberry pi instead?

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    3. Yes, the amp is being powered from the proto-board connected to wall power. A 2A power supply feeds the proto-board.

      The max power raspberry PI 5V can supply:
      Model A: 1000 mA - 500 mA -> max current draw: 500 mA
      Model B: 1000 mA - 700 mA -> max current draw: 300 mA
      Source: http://elinux.org/RPi_Low-level_peripherals#Power_pins

      The MAX98306 (IC in the amplifier) data sheet says max In/out current is 800ma. Therefore, I did not try powering the amp from the 5V pin on the PI and don't recommend it.

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