Musings and Hobbies

Recycled Volvo Amps provide 130 watts of sonic power for the desktop

2010-07-18T20:12:00.001-07:00

A couple weeks ago I was cleaning my garage and came across these Volvo amplifiers from my 86 Volvo 760 (wonderful car worth every penny!) I was about to trash them but I decided to build a portable desktop power amplifier.
The smaller amplifier is HA-3121 and rated at 25 Watts per channel, the rear amplifier HA-3141 is rated 40 watts per channel. Ok, a 130 watts desktop power amplifier!
Since I was in the recycling mood I salvage an assortment of RCA inputs, speaker connectors, switches, LEDs, from my garage cleanup. I also used rails and nuts and bolts left over from my flat panel TV mount.

I temporarily hook up all the wires to a 12 volt wall transformer and was disappointed that nothing works (very low current). I then quickly connect a 12 automotive battery and only the HA-3141 came alive, the HA-3121 did not. The problem was traced to a faulty relay, probably the reason the amps were out of the car in the first place. A few taps on the relay and a few minutes of activating deactivating it and now the relay works trouble free.

Bolted the rails to the main power amp.

Bolted the secondary amp to the main amp. The main amp had a mounting plate allows for a 1/4 inch air gap.

A piece of Plexiglas foundation for the input, power and output connectors.

The 12 automotive battery provided plenty clean current which the wall transformer could not. I hooked up my bench top power supply recycled from a computer power supply. The plans are here http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
*** Of course be very careful when working with electricity, line voltage can and will kill! ***
The computer power supply yields approximately 11.7 volts plenty of oomph as I take the amplifier to max. There is a limited amount of voltage available in an automobile (approximately 13.5 volts). This means that the amplifiers have fewer than 12 volts to apply to the speaker leads after factoring internal system resistance. If we have only 12 volts to drive into a speaker, there may not be sufficient volume output if the speaker has high impedance; therefore I wire my 8 ohms speakers in parallel for 4 ohms to maximize the output power to the speakers. (Ohm’s law)

Wiring for the HA-3121
Speaker wires

left output: green/yellow -
left output: green/white +

Right output: gray/yellow -
Right output: gray/white +

Power
Yellow constant 12 Volt
Black (thick) Negative ground
black (small) not connected

Input (shielded bundle)
Orange 12 volt remote on

left input: Blue (contains 2 wire, unshielded is negative)

Right Input: Green (contains 2 wire, unshielded is negative)

Ignore all other wires ( red, black etc)

---------------------------------------------------------------------

Wiring for the HA-3141
Speaker wires

left output: Black -
left output: Yellow +

Right output: black -
Right output: white +

Power
Yellow constant 12 Volt
Black (thick) Negative ground
black (small) not connected

Input (shielded bundle)
Orange 12 volt remote on

left input: Blue (contains 2 wires, unshielded is negative)

Right Input: Green (contains 2 wires, unshielded is negative)

Ignore all other wires ( red, black etc)

Arduino, Vex receiver and signal splitter

2009-11-22T09:32:00.000-08:00

The Setup : The Arduino powers the vex decoder via 5v which in turn powers the vex receiver, no other external power required.

5 volts is sent from the arduino to the signal splitter via the positive output of one the the channel connection. The signal splitte ground connection is connected to the arduino ground.
The 5 volts also flows to the receiver - splitter connection.

Vex Properties via the signal splitter
Channel 1,2,3 & 4
range : from 753 to 2241
Center stick position varies between 1480 and 1510

Channel 5 & 6 (digital Channels)
range : off = 753 on = 2241

arduino Code

/*
nikitanicholas@gmail.com
Use freely

Vex transmitter & Vex receiver kit : http://www.vexrobotics.com/vex-robotics-transmitter-receiver-add-on-kit.shtml
Vex signal splitter : http://www.vexrobotics.com/vex-robotics-signal-splitter.shtml

Vex Properties via the signal splitter
Channel 1,2,3 & 4
range : from 753 to 2241
Center stick position varies between 1480 and 1510

Channel 5 & 6 (digital Channels)
range : off = 753 on = 2241
not activated: 1500

The Setup
The Arduino powers the vex decoder via 5v which in turn powers the vex receiver, no other external power required.

*/
#define channelNumber 6 // 6 Channels on the vex

int value[channelNumber];
int val;
int adrinoPin;
void setup()
{
Serial.println("init");
Serial.begin(57600); //Serial Begin
pinMode(2, INPUT); //Pin 2 as input
pinMode(3, INPUT); //Pin 3 as input
pinMode(4, INPUT); //Pin 4 as input
pinMode(5, INPUT); //Pin 5 as input
pinMode(6, INPUT); //Pin 6 as input
pinMode(7, INPUT); //Pin 7 as input

}
void loop()
{
adrinoPin = 2; // start with pin 2
Serial.println("looping......");

for(int x=0; x<=channelNumber-1; x++)//Loop to print the channel readings
{
if (pulseIn(adrinoPin, HIGH) == 0 )
{
Serial.print("No signal on Channel" );
Serial.print(" ");
Serial.print(adrinoPin -1); //Print channel
Serial.println("");
}
else
{
Serial.print("Channel" );
Serial.print(" ");
Serial.print(adrinoPin -1); //Print out the channel number
Serial.print(" = ");
//val = .pulseIn(adrinoPin, HIGH);
val = normalizedPPM(pulseIn(adrinoPin, HIGH));
Serial.print(val); //Print out the value
Serial.print(" ");
}
value[x]=0; //Clear the array after printing
adrinoPin++; // increment pin count

/* Future Project
* Output PWM voltage based on Vex signal pulsein
* The pins marked PWM (pins 3, 5, 6, 9, 10, and 11) can be pulsed using the analogOut()
* Pulsewidth is a value from 0 - 255. 0 corresponds to 0 volts, and 255 corresponds to ~5 volts.
* Every change of one point changes the pseudo-analog output voltage by 5/255, or 0.0196 volts.

When no signal is received from the Vex transmitter or stick prosition are centered
the following should occur : arduino output 50% duty cycle corresponding to approx. 2.5v ( PWM to output pin is 127)

When Pulsein is between 1550 and 2200
the following should occur : arduino output 75% duty cycle corresponding to approx. 3.5v (PWM to output pin is 178)

When Pulsein is between 750 and 1450
the following should occur : arduino output 25% duty cycle corresponding to approx. 1.5v (PWM to output pin is 76)

Available pins 9, 10 , 11
*/

}

Serial.println("");

delay(500);

}

/*
Smoothing out the center channel ( software trimming)
*/
int normalizedPPM(int ppm)
{
if ( ppm > 1480 && ppm < 1510)
return 1500;
else
return ppm;

}

Robot building

2009-11-21T18:41:00.000-08:00

In my earlier blogs I hinted on a robot built with a posting of
Arduino, Vex receiver and signal splitter.

Electric wheelchair inspection and breakdown

I picked up a broken electric wheelchair Jet3 Ultra from the local flea market for $50. It was complete with a broken chair support but not running. I began to strip it down to the bare essentials i.e. remove the seat and support, leg rest arms, fenders and bumpers. I replace the fuse and tinkered around with the controller and finally got it to power up. Here you have it! a complete, powered, really sturdy robot base that can really cut down on development time.

High Level design parameters

1. Keep original wheel chair controller: The controller have a number of built in safe guards such as locking the wheel when not active, power on test, speed control especially when turning at high speeds.

2. Incorporate a wireless control : Arduino, Vex receiver and signal splitter.

3. Computer control: Automation with various sensors such as digital compass, accelerometers, vision, maps, internet, LCD display and whatever I can throw at it.

The original motor controller

The key to success in interfacing with wheelchair motor controller is to tap into the joystick input.

First, we will need a switch to flip between joystick and an alternate source of input: computer and or remote control.