Thursday, January 26, 2012

Reuse Scrapped VU meter as Voltage and Ampere meters

From scrapped HIFI equipment i saved two VU meters and wil use them as voltage and ampere meters for power supplyes. To messure ampere i use a pololu pcb with allegro's 30 amp hall effect linear current sensor.

In one VU meter they use two chips : LB1412 from sanyo

Specification for this chip:

  • Bar-shaped display of input level by means of 12 LEDs
  • High-order 5 dots with peak hold
  • Built-in oscillator for peak hold reset
  • Requires 1 pce. each of external C, R
  • Uses either oscillator at the time of stereo operation
  • Capable of also resetting manually
  • Capable of constant-current driving low-order 7 dots (green LED)
  • Constant-current value variable with an external resistor
  • Lower current drain available by connecting green LEDs in series
  • Built-in input amplifier
  • Requires no other light-up level adjustment than adjustment for 0 dB
  • D1 error: within ±3 dB of 20 dB
  • Supply voltage range : 10 to 16 V

In the other VU meter there is a also two chips: panasonic Dual 5-Dot LED Driver Circuit AN6888 and AN6888

AN6888/6889 is an IC driving 5 ´ 2-ch LED and is capable of logarithmic bar graph display for input signal.
Incorporating high gain rectification amp. enable to apply VU/Signal meter widely.

Because the output is the constant current pull-in type, the constant current value can be variable by external resistance. n Features

I am not sure what the difference is between the two types but i found a schematic:

Specification for this chipset:

  • Wide range of operating voltage : VCC (opr.) = 5V ~ 16V 
  • Power consumption can be reduced due to series connection of LEDs
  • Wide range of constant current : 5mA ~ 25mA
  • Built-in high gain amp. : GV = 26dB typ.

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