Injector Pulse Width Monitor with LM324 ,LM3914

The schematic for the pulse width monitor. The heart of the circuit is the transistor current source which charges cap C10 to form an integrator. The theory is that the cap is charged and the voltage across it increases linearly for the amount of time that the injector is energized. As the injector is switched off the voltage in C10 is stored in cap C9 and then C10 is reset to 0 volts to get ready for the next cycle. The output of the circuit is the voltage across cap C9, this voltage is fed directly into U3 the bar graph chip to be displayed as a value between 1-10 on the LEDs. Potentiometer R31 sets the charge rate on C10 and basically sets the max injector on time that can be displayed.

Download this schematic diagaram.

download datasheet the semiconductor component. (PDF Format)

1. LM324

2. LM3914

3. CD4058

4. LM7805

5. MN3206

6. MN3906

7. 2N2222

8. IN214

9. IN5233

Injector Pulse Width Monitor with LM324 ,LM3914 - [Link]

Temperature Monitor with IC LM741 or LM301

Using a thermistor in the position shown makes a heat activated sensor. A change in temperature will alter the output of the opamp and energize the relay and light the LED. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.

Download this schematic.

Download semiconductor parts datasheet. (PDF Format)

1. LM741

2. LM301

3. BC182B

Temperature Monitor with IC LM741 or LM301 - [Link]

9v Battery Voltage Monitor using a LTC1440 Comparator

This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also contains a 1.18v reference diode. In standby mode, the circuit draws only 4uA.

Battery Monitor Circuits
Master Schematic Category List - David A. Johnson, P.E.