USB-connected Buttons That Can Be Used to Simulate Episode of a Music Game Show

Some time ago I was asked to manually press the space bar of a regular keyboard after noticing press of a large button, that was not connected to anything, by a future contestant in Polish version of Name That Tune. Space bar was stopping playback of a game show episode during training session In response to this inconvenience, I used V-USB library, running on a 8-pin AVR MCU, to make a simple USB HID keyboard. Base project for this keyboard’s software was EasyLogger.

In addition to the space bar, this keyboard has 4 additional buttons, witch can be used to send 6 additional commands that control media playback. It is possible, because pairs of buttons are connected to the respective analog-digital converter’s multiplexer inputs. Each of the two active ADC channels is connected to the button-operated voltage divider that has 4 possible states, two buttons can be pressed simultaneously in order to achieve fourth state. Commands are tailored specifically to act as Celluloid media player’s shortcuts.

You can download source code, schematic, PCB, etc. for this project here:

spaceplus_all_files_v1.zip, mirror, SHA256: c5cd433803dea3f2ad4aed54d82928aca95911571b3d25a97f9459a12b65d10b

Parts and materials:

1. ATtiny45-20PU microcontroller (8-PDIP, ATtiny85-20PU will work just as well)
2. 8-pin DIP IC socket (300 mil body width, 0.1 inches [2.54 mm] pin pitch)
3. 2x 3V6 Zener diodes in DO-35 THT package.
4. 3mm LED (I used clear white one that might have been too bright, you can regulate LED’s current by changing value of R4, LED with diameter of 5 mm or slightly different shape should fit too)
5. 4x 6x6mm tactile switch buttons (THT)
6. large momentary push button switch (mine was PROMET NEF30)
7. 2x 68 ohm 1/4W resistors
8. 2k2 ohm 1/4W resistor
9. 1k ohm 1/4W resistor
10. 2x 10k ohm 1/4W resistor
11. 2x 15k ohm 1/4W resistor
12. 2x 22k ohm 1/4W resistor
13. 100 nF ceramic capacitors
14. 10 uF electrolytic capacitors
15. prefboard (50mm x 70mm, min 18 x 24 hole array), alternatively, you can etch copper clad board yourself and drill holes
16. cable that ends with USB Type-A plug and can have conductors on the other side soldered to the prefboard (I used 1.9 m of 4-conductor ribbon cable manually soldered to USB connector)
17. 2-conductor wire that will connect large push button with the prefboard (in my case it was too long piece of ribbon cable)
18. few pieces of copper wire (UTP cable can be a great source of wires)
19. insulating tape
20. small piece of cardboard
21. 4x wood screws that have a length of around 10 mm and diameter comparable to 1.2 mm (prefboard used by me had 4 mounting holes with ~1 mm diameter, I was able to use aforementioned screws to mount prefboard onto flooring panel that was main structural element)
22. 3 pieces of wood (or similar material), and screws that are going to make them into structure. I actually did not make it, I only added electronic circuit that provides USB connectivity. One of the the pieces of wood had 26 x 20 cm, and was a piece of flooring panel (plywood would work as well). Other two pieces were 5 x 5 cm “beams”, that had a length of of 20 cm. Large circular hole was made, into which large momentary push button switch can be installed (30.5 mm diameter is recommended size for NEF30).

Tools:

1. diagonal cutter
2. pliers
3. flat-bladed screwdriver
4. small phillips screwdriver
5. tweezers
6. utility knife
7. center punch
8. hammer
9. multimeter
10. soldering iron or gun
11. solder
12. soldering flux (I used RMA class, flux gel intended for SMT assembly and repairs, that came in 1.4 cm^3 syringe)
13. desoldering wire
14. helping hand with crocodile clips
15. pencil
16. set square
17. ruler
18. AVR programmer (standalone programmer like USBasp or you can use ArduinoISP)
19. breadboard and jumper wires that will be used to program microcontroller outside of PCB (or any other tool that can achieve this goal)
20. woodworking tools that can be used to cut structure's parts (saw [jigsaw may suffice], drill, drill bits, hole saw, file, plus something that can hold the pieces in place [F-clamps for instance])

Construction of this device requires use of moderately dangerous tools and may cause harm or damage to property. You build and use described device at your own risk.

Solder all electronic components to the prefboard (except Attiny45/85, it will be later put inside a socket). Use copper wires (0.5 mm diameter ones from UTP cable should be perfect, leads cut from components will also work) to make electrical connections between components.

If you prefer to make your own PCB I also provide .svg files (board dimensions are 63.50 x 48.26 mm). Single sided copper clad board should suffice, as there are just two connection on the front side (they can be made with two wires), so files for the front side are provided mainly for the benefit of connection identification.

Four conductors of ribbon cable (with improper color-coding) were singled out and stripped out of insulation on both ends of the cable. You can fix end of the cable in position with the helping hand’s clip. On the one end you have to tin conductors, insert USB plug’s housing, and solder pins to the conductors. Housing can be then shifted to a position enclosing rest of the connector, and secured in place with tape. Other side of USB cable was prepared to installation in prefboard’s holes just by tinning conductors.

Two conductors of ribbon cable were used to connect large push button switch with prefboard. On one side long portions of exposed tinned conductors were bend backwards and improperly attached to insulation by too large heat shrink tubing. This reinforced side was to be installed in button’s screw terminals. Other side had short tinned conductors that can pass through prefboard’s holes.

Both cables were soldered to rest of the circuit. Prefboard’s connection to cables was additionally reinforced with short wires, that had insulation in their centers remaining, being enveloped around ends of ribbon cables, and soldered to prefboard (electrical connection to ground was made).

After soldering, I attached a piece of cardboard to the back of the board. I tried to do it use double-sided tape to make cardboard more sticky, but it didn’t work very well. Back of the prefboard was much too uneven. The role of cardboard was to deform when crushed by sticking out leads, allowing more uniform distribution of pressure when board is mounted with tightened screws.

Connect ATtiny45 or 85 to your favorite programmer, you can use a breadboard and jumper wires to do it. Open your favorite AVR dev tool, change fuse bits to H:DD, L:E1 , and write one of .hex files to microcontroller FLASH memory.

Following commands should install software necessary to program microcontroller, and modify it if needed in Debian-based GNU/Linux distribution.

Next one will change fuse bits, so that higher clock speed can be achieved (-B 8 part allows programmer to work with default clock).

This one will write firmware into Flash memory.

Number “45” can be replaced in above commands by “85”, if necessary. Modifications of source code will require use of makefile, that is provided in the spaceplus_all_files_v1.zip archive.

When programming was done, DIP IC could be inserted into appropriate socket.

I used set square and pencil to mark where screws will be located at the flooring panel (main structural element), then center punch to make indentations in the panel, allowing easy and precise mounting of the screws (large screw was used to make indentations a little bigger). Four screws were inserted into prefboard’s mounting holes and driven into flooring panel.

Large momentary push button switch was attached to the ribbon cable by inserting two exposed tinned conductors into appropriate places and tightening the screws. Ribbon cables were additionally secured in place with pieces of insulation tape.

Most computer with USB connectors should detect this device as regular keyboard, after it is inserted into proper receptacle.

Total of seven key combinations can be achieved with five physical push buttons. They are specific to Celluloid media player, so another use cases may require changes to source code and recompilation. I will list combinations bellow:

SW1 SPACE → space bar (pausing and resuming playback)

SW3 GO_BACK → right shift + , (<, go backward in the playlist)

SW2 GO_FORWARD → right shift + . (>, go forward in the playlist)

SW4 BACK_1S → right shift + left arrow key (exact seek backward 1 second)

SW5 FORWARD_1S → right shift + right arrow key (exact seek forward 1 second)

SW3 GO_BACK + SW2 GO_FORWARD → down arrow key (seek backward 1 minute)

SW4 BACK_1S + SW5 FORWARD_1S → up arrow key (seek forward 1 minute)