I like your design. I designed a universal flashing LED in 1975 and has been used on various vehicles for 4 decades.Hi, I've been looking for weeks and its doing my head in!
All I'm after is a VERY simple circuit, just one led that lights up when the fuel gets low on my bike. (making a custom dash using the "Veypor")
I'm usually pretty good with electronics ect, but i need some help with this one!
I've been searching for ages and only come across crazy complex (for a noob) circuits with time delays and 100,000 led light bars!
Is this anywhere near a working cercuit?!
What i've "tried" to do is have the led switch on when the fuel drops below 90Ω this should be @ 6.2v that the zener is at. So when the fuel drops the zener has more voltage and switches the led on.
Dont realy need any sort of 'time delay' to combat fuel sloshing around and continualy ficking the light on and off. This is because as it stand the fuel guage sits at 'full' 90% of the time anyway, its not till the last 30km or so that needle moves down. (and when it does its a rapid decent!)
Also any feedback on the resistor ratings would be very apriciated.
Click on pic below
View attachment 11998
My design self-adjusts to various battery or alternator voltages. It can be used on different gas tank voltage wiring as shown.
Some vehicles use an empty tank signal at full voltage. Some vehicles use a full tank signal at full voltage. Just flip pins 2 & 3 as needed.
I don't have a flasher circuit. The LED flashes in real time when any gasoline wave forms in the gas tank and bumps the float up or it goes down, the LED changes its lit state.
If you drop below the variable voltage barrier or trip point voltage, the LED stays on without any waves, like if parked.
If I am on 'fumes' in a remote desert (yes it happened in 1986), I tap my brakes to create a wave and I see the always ON LED indicating low fuel, but a wave will turn it OFF as if it was 'flashing'. That ability to flash in real time on fumes indicates I have a quart or two in my gas tank. Anything that causes a wave peak and trough will make the LED flash in real time. To be clear, any wave peak makes the LED turn OFF. The trough or wave valley makes it turn ON.
This circuit can be adapted to any vehicle or motorcycle with a flaot that sends a voltage to any gas guage. I am not sure about series dual gas tank setups like a Subaru uses.
The input resistance of the 741 op-amp with a single voltage supply, is of the order of 2+ megohms. It will not load down any voltage from the gas tank circuit or float setting. I measured one 741 at 5+ megohms. It is essentially a vacuum tube voltmeter, a VTVM, high impedance perfect potentiometer knock off.
My Universal Real Time Low Fuel Indicator LED Circuit from 1975. The image is a bit dated but the information is there.
One problem was the puny 21 millicandles (mcd) of old LEDs. I had to over drive old LEDs with a short duty cycle to get it brighter. That shortens an LED lifetime.
This problem was fixed and changed recently by using Super Bright LEDs of the 28,000 mcd or 34,000 mcd type.
These super brights have a voltage drop of 3.1 - 3.2 volts. At 10 ma, you WILL see these flash in bright sunlight.
I use this circuit in duplicate to flash either turn signal direction inmy vehicle and my LED indicates 'an in-use reminder' because a newer small relay system like a relay system from Denso, et al, are just too quiet with a radio on and a window down.
So, the 220 ohm resistor should be about 1K to 4K. To run higher currents than the 741 can sink, you will need to install a 2n2222 type transistor at the 'bottom' of the LED and put the emitter on ground. The 741 output pin 6 should have enough voltage to turn on the NPN base with a positive voltage.
I use 4.5 K. Yes, the current is lower through the new LED but knocking it down from 30,000 mcd to 20,000 or 5,000 mcd is going to be seen in bright sunlight anyway.
The problem is the 741 datasheets just say the Short Circuit current is typically 25 ma. Well, how about the typical test circuit or recommended clearly stated sinking current? Be safe and add the NPN transistor. They are cheap and general replacement for almost any NPN transistor. ECG123A/NTE123A, 2N2222, PN2222, MSPA42, etc. all work. If you can't turn the NPN transistor totally OFF and put it into cutoff, add a 1N915 diode between the emitter and ground to cheaply raise ground. I think the 741 will sink 20-25 ma but I have never seen that stated as typical. Never short pin 6 directly to ground on a 741. I will be a goner.
Your circuit is just about the same but I wanted to show and explain how mine actually works for some readers. Most of this applies to how your circuit that works with the Zener.
HTH, and JMO,
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