Automotive Ammeter As a current meter for automobiles. It replaces the standard ammeter with a very effective voltage recording system. Digital presentation through 9 Leeds. Scale with 0 to the center.
Summary
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- 1 OPERATION
- 2 LIST OF COMPONENTS
- 1 RESISTORS
- 2 CAPACITORS
- 3 SEMICONDUCTORS
- 3 NOTES
- 4 TECHNICAL MANUAL
- 5 Sources
FUNCTIONING
When current flows through the cable that connects the negative of the battery with the chassis, a voltage drop occurs on that cable. This voltage is used in this circuit to determine the charge or discharge current. The voltage produced in cable that goes between the negative of the battery and the chassis, enters the circuit through the voltage divider R1, R2 (D1-D2 protect the circuit from overvoltages at the input). The voltage from the midpoint of the voltage divider enters the gate of T1 (T1 and T2 constitute a differential amplifier). The output voltage of the differential amplifier enters the inputs of the op amp IC1. This integrated circuit is connected as a variable gain amplifier (the gain is varied with R7). The output of this amplifier enters a voltmeter to Leeds, built based on the use of an integrated circuit type LM3914, which is a 10 linear step voltmeter. The zener D3 diode gives stability to the two amplifiers and C1-C2 decouples the noise from the power supply to the circuit
COMPONENT LIST
RESISTORS
- R1 = 12 Kohms (brown, red, orange)
- R2 = 220 Kohms (red, red, yellow)
- R3 = Preset 10 Kohms
- R4 = R5 = 3.3 Kohms (orange, orange, red)
- R6 = 1 Kohm (brown, black, red)
- R7 = Preset 100 Kohms
- R8 = 120 Ohms (brown, red, brown)
- R9 = 2.2 Kohms (red, red, red)
- R10 = 4.7 Kohms (yellow, purple, red)
- R11 = R14 = 1 Kohm (brown, black, red)
- R12 = 820 Ohms (gray, red, brown)
- R13 = 3.3 Kohms (orange, orange, red)
- P1 = Potentiometer 50 Kohms Linear
- RA = RB = RC = 1 Kohm (Brown-Black-Red)
CAPACITORS
- C1 = 100 nF (disk)
- C2 = 10 µF 35 V (Electrolytic)
SEMICONDUCTORS
- T1 = T2 = 2A244 / 45
- D1 = D2 = 1N4148
- D3 = D13 = Zener 5.1V ½ W
- D4 = D5 = D11 = D12 = Red Led
- D6 = D7 = D9 = D10 = Yellow Led D8 = Green Led
- IC1 = TL081
- IC2 = LM3914
NOTES
The input terminal should be connected near the negative battery terminal, but not on the terminal itself.
- The ground terminal must be connected in the same place that the wire coming from the negative battery terminal (chassis, block, etc.) is connected to ground.
- The positive wire should be connected to 12V at a location taken after the ignition key.
TECHNICAL MANUAL
- The LEDs must be mounted in such a way that they protrude from the rest of the components. They can also be bent to the front or welded on the copper side of the plate. In this case, the precaution of connecting them correctly must be taken.
