LED Voltage Level Indicator
The applications of this circuit are FM tuning
indicator, Stereo Balance Indicator, Wire T2 like
T1 then we get two channel inputs and battery
a Circuit Design
This circuit is derived from a Siemens
Application Note 1974. This circuit uses common
components of today. The circuit is here as it is
of high educational value.
You can 'simulate and test' or 'wire it up and
try' and let me know how it worked. The Circuit is
also a simple analog to digital converter. You can
use optos in place of LEDs.
Monitor for your Boat or Car
T1 and T2 make a differential amplifier. T3, T4
and T5 driving the LEDs are comparators. Now to
learn more on how they work you have to study
circuits at 4QD-TEC.
When input voltage is increased T1 is turned on
which leads to more base current for T3 which
Lights LED1. When input voltage is less T2 turns
on as it gets a better base current from P3 which
turns on LED2 via T4. When both LEDs are off T5
gets biased as no drop across R5 which lights the
LED3 thru T5 hopefully.
What you need to know is a small current Ib thru the
base-emitter path in the direction of the emitter
arrow will lead to a large Current Ic thru the
emitter-collector path in direction of arrow. Ic = B
* Ib where B - beta is the DC current gain, it could
Current Source and MOSFET
Beta is different in each transistor you buy and
varies with the test conditions and even with
temperature and age. The LED1 and LED2 will indicate
above or below Limits set by P2 and P1. The Limit
Threshold itself is set at P3 i think. LED3 will
light when Hi LED and Lo LED both are off.
Toss with LEDs
Running LED, Random Results, Decade Counter and
Clock. Weigh the Pros-n-Cons, Take a Balanced
This can be built with one 555 timer and a CD4017.
Use the pin 5 to connect to a cap you charge with a
pushbutton or gate like CD4093 to turn off 555 using
pin 4 after a cap discharges. This may simulate a
Press the Red Button
above, wait, the LED will spin fast and slow
down,then come to rest at the random decision LED.
The above Toy may need a VCO and a Ramp Generator as
well. Start with this design 555
and CD4017 Running Lights use the 4th LED
output to reset the counter.