The interface electronics resides in a narrow area down the right hand side of the chassis. This must clear the right hand side of the optical drive. Additional brackets support the circuit boards.
This small board has several purposes in life. It controls the Power and LED indicators. It also controls the Power Relay, located in The Dog Box. An opto isolator ouptut is used to control amplifier muting.
The Power LED is fed from the Computer Power Supply +5V rail via R6, which was chosen to match the brightness of the Message and HDD LEDs.
The Computer Power Supply +5VSB rail is permanently active even when the system is shut down and is used to power U1 - a quad comparator IC with open collector outputs (LM339).
U1B detects when the system is shut down by comparing the Computer Power Supply +12V rail voltage with the +5VSB rail voltage. The output of U1B acts as a switch to control the Standby LED. The LED brightness is determined by R5.
U1D detects when the system is on by looking at the Computer Power Supply +5V rail. U1A detects mains failure by looking at the Computer Power Supply Power Good signal. The open collector outputs of these two comparators are connected together and pull to ground when the +5V rail and/or Power Good signal goes low.
When the system is first powered up, a timer consisting of R11, C3 and U1C delays the activation of the Power Relay for approximately 1 second.
When the system is powered down or the mains drops out, U1D and/or U1A reset the timer by rapidly discharging C3 and the Power Relay is turned off instantly. Once this happens, the timing cycle must complete before the Power Relay can be turned back on again.
The Power Relay drive circuitry is powered by the Computer Power Supply +12V rail via R16. When the Power Relay is off, C4 is charged to +12V. When the relay is first activated, full power is applied to the relay coil, due to the charge stored in C4. The current through the coil at this instant is approximately 35mA. Relays only require about one third of the current to remain closed after they are activated. Due to R16, the current drops to approximately 20mA to conserve power. R17 reduces the maximum current through the opto-isolator.
This board drives the work lights, chassis illumination, the HMV logo and speaker enclosure area illumination.
Each channel is a switchable current source, capable of delivering up to 100mA. A channel is switched on by grounding its input. A PWM signal can be used to control the brightness of each channel.
The 10 Channel LED Driver Board is controlled by the LED Controller Board, described later.
The maximum current (IMAX) for each channel is chosen to suit the type of LEDS used in that channel and is set by resistor Rn03 as follows:Rn03 = 0.6 / IMAX
Since the LED drivers are powered from the +12V computer rail, the maximum number of LEDS that can be wired in series on the same channel depends on the type of LED. Red, orange and yellow LEDs usually have a forward voltage drop (VF) of around 2.2 - 2.5V and there can be up to 4 on the same channel. On the other hand, green, blue, aqua and white LED's have a VF of around 3.3 - 3.5V, limiting the maximum to number to 3.
Assuming either 4x LEDs @ 2.2V or 3x LEDs @3.5V, this represents a regulator efficiency range around 73% to 88%.
For higher current channels, the minimum number of LEDs should also be considered. For example, for a 70mA channel there should be a minimum of 3 LEDS to limit the heat dissipated in the driver transistor (Qn02). Note that with PWM control, the worst-case heat dissipation is when the LEDs are 100% on.
The following types of LEDs were used in this project. These were all obtained from Jaycar Electronics and the part numbers are Jaycar catalogue numbers:
| PART No | COLOUR | nM | VF | IF mA | mCd |
| ZD-0283 | Red | 625 | 2.2 | 70 | 35000 |
| ZD-0285 | Orange | 605 | 2.2 | 70 | 35000 |
| ZD-0284 | Yellow | 590 | 2.2 | 70 | 35000 |
| ZD-0282 | Green | 525 | 3.3 | 50 | 60000 |
| ZD-0178 | Aqua | 505 | 3.5 | 30 | 7000 |
| ZD-0281 | Blue | 470 | 3.3 | 50 | 18000 |
| ZD-0195 | White | 3.2 | 30 | 20000 | |
| ZD-0280 | White | 3.3 | 50 | 40000 |
All LED's except the ones mounted on the HMV Logo Board are on sockets to allow for the option of changing colours.
This is the current lineup:
| Cct | Description | IMAX | Rn03 | LEDs |
| 1 | Work Lights | 27mA | 22R | 3x ZD-0195
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| 2 | Chassis Illumination | 27mA | 22R | 1x ZD-0284
1x ZD-0285
1x ZD-0178
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| 3 | HMV Logo - R | 7mA | 91R | 3x ZD-0283
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| 4 | HMV Logo - G | 50mA | 12R | 3x ZD-0282
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| 5 | HMV Logo - B | 13mA | 47R | 3x ZD-0281 |
| 6 | Speaker Rear - R | 67mA | 09R | 3x ZD-0283
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| 7 | Speaker Rear - G | 50mA | 12R | 3x ZD-0282
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| 8 | Speaker Rear - B | 50mA | 12R | 3x ZD-0281 |
| 9 | Speaker Rear - W + B | 50mA | 12R | 2x ZD-0280 1x ZD-0281 |
| 10 | Speaker Front | 67mA | 9R | 4x ZD-0284
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| - | Standby Indicator | 1.5mA | - | 1x ZD-0285
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| - | Power Indicator | 10mA | - | 1x ZD-0282 |
| - | Message Indicator | - | - | 1x ZD-0284
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| - | HDD Indicator | - | - | 1x ZD-0283
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Overall, there are 35 high efficiency, high power (and high priced!) 5mm LEDs used in this project.
For the HMV Logo, there are 3 LEDs for each colour. By adjusting the relative brightness of the red, green and blue channels, it is possible to obtain almost any colour. There is plenty of light for the HMV Logo so I adjusted the current down to get the correct balance between the LED channels. On the other hand, I set the LEDs for the speaker at their rated limit to get maximum light from these.
The chassis power wiring was covered in Section 6 - Power Distribution. Other Chassis wiring includes LEDs, connectors, switches, the Computer Motherboard, Computer Sense Board and 10 Channel LED Driver board.
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Channels 1 and 2 of the 10 Channel LED Driver Board are used for the chassis lighting.
 Testing the work lights
 Illuminated chassis viewed through dial
cutout
The main purpose for the work lights is to assist in connecting things to the computer and the rear chassis connectors. In my long-term plan, the chassis illumination will only be seen from the back of the unit. In the short term, until I find a suitable touch screen it will also be seen from the front through the cabinet cutout for the old tuning dial. Both of these sets of lights also throw light onto the wall behind the unit and can be part of the overall lighting effect. |
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TESTING THE LED CIRCUITS
 In addition to being controlled by the LED
Controller Board, the Work Lights and Chassis Illumination circuits
(channels 1 & 2 of the 10 Channel LED Driver Board) can be turned on
manually by the Dial Lamp Switch.
 Temporary test jig for controlling the last 8
channels of the 10 Channel LED Driver Board manually without the LED
Controller Board. This can only switch individual channels on
and off.
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In addition, the Power LED (driven by the Computer Power Sense Board), the Message and HDD LEDs (driven directly by the computer motherboard) are mounted on the chassis but shine into the speaker enclosure area.
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All of the low voltage cabinet wiring is in one loom, connecting via a single DB25 connector to the main chassis. I pre-made this loom, cut and shaped to fit the cabinet. When the speaker enclosure area is sealed, it will not be removeable! This includes wiring to:
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The Standby LED (driven by the Computer Power Sense Board) is mounted directly on the cabinet in the chassis area but shines into the speaker enclosure area.
Ch 3-5 of the 10 Channel LED Driver Board are wired to a socket which connects to the HMV Logo Board inside the Speaker Enclosure.
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Ch 6-10 of the 10 Channel LED Driver Board are wired to 10-way 0.1" (2.54mm) receptacles, mounted in the 4 front corners of the speaker enclosure area and hidden from view. These sockets are wired in series and up to 5 LEDs can be inserted into each of these sockets. There can be up to 4 LEDs per channel only if they are red, orange or yellow. For other colours where there can only be 3 LEDs per channel, the 4th position must be by-passed with a link. Using this socket system allows LEDs to be easily changed and allows versatility in the final lighting setup. If necessary, an individual LED could be relocated by plugging in a 2-pin header and extension cable. |
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 Constructing the Cabinet Wiring Harness
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 HMV Logo Board
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 Testing the speaker enclosure area
circuits
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