Load drivers sure are useful little buggers.

 

Load drivers sure are useful little buggers.

I've been using them as industrial-strength combinational logic since the 70'.

ak

 

@edgeb I made a mistake in post #40, you will need to keep the 5 volt regulator, I forgot that that the CD4020BE does not have logic level inputs...sorry.

 

Here is the full circuit with the divider and LED driver. Because the 2003 has an open collector output, U1F acts as a logic level translator. With it, the 5 V input signal can drive the 12 V counter.

ak

 

hi edge,
Please let us know which circuit you have decided to use.?

When a TS posts a circuit and asks for guidance why it does not work as he expected, I try to fix the 'bugs' in his/her circuit in order to get the required performance.
The TS learns what mistakes he has made and what changes are required, in this way the TS learns and gets some personal satisfaction

Often helpers post an alternative circuit, if the TS copies the circuit as posted, he will probably will have learnt nothing and have no idea how the circuit works.

E

 

Once this model is working I may also build some of the other designs as posted by the other helpers.

That's certainly educational. If you want to experiment with a minimal version of a missing pulse detector you could try this:-

 

hi edge,
A sim of your circuit, frequency sweep input from 90Hz down to 40Hz over a 10Sec period.
E
The elements in the dotted rectangles are for the simulation.

 

Hi Eric

I designed the circuit. You’re right - if there’s no AC input to the counter, and from there into the 555, it won’t latch. I designed it that way. But by starting the pump, via the relay, fuel will flow and the AC input will be activated.

The momentary switch manually activates the 555, and via the transistor, it closes the relay, which not only powers the pump but also feeds current into counter and the 555. Doing so basically the puts whole thing live. I guess you could say it’s a latching circuit If you then release the momentary switch, it stays live until the first missing pulse sets the 555 output low, which then opens the relay, killing power to the counter and the 555, and that way the whole system dies until you start it again.

I didn’t want to use a pulse-based relay because I want the system to stop pumping if there is any fault at all - it’s for an aeroplane and theres no room for error. It’s better for fuel not to pump
Than for it to carry on pumping when it shouldn’t. So I only want it to pump while there’s current to the relay.

The circuit functions exactly as designed - which is a small miracle, given my inexperience.

I’m now trying to design some fault tolerance into it and the one potential pitfall I see is if there’s a break in the line from the fuel flow transducer into the circuit. (The transducer is right at the front of the fuselage and my instrument panel where this circuit will be housed is about 2m towards the tail).

Hence my post.

I hope that makes sense?

Thanks!

Hi

Just curious...but what happens if the relay energizes and starts the fuel flow even though a fault has occurred?

eT

 

hi,
Measure the Voltage on the 2N2907 Emitter.
E

 

Hi eT

This circuit will be used in a fuel transfer system, pumping fuel from a wing tank to a center tank.

If the source tank runs dry, flow rate would drop and therefore the system should shut down the pump. If there was an error and the pump continued to run once the source tank ran dry, then the pump would continue pumping air. For a few seconds at a time that’s not a problem but over longer periods it can cause the pump to heat up. Not good on an aircraft fuel system, as you can imagine.

If it the reduced flow rate was caused by a blockage in the fuel pipe, as another example, then the pump would be straining, leading to heat build up. Also not good.

Does this answer your question?

yes...thank you.

I’ve worked maintaining small commercial aircraft and was wondering if this DYI is a safe thing to do, knowing all the failsafe redundancy put into Aircraft systems...

thanks for your reply...

 

hi edge,
I guess you have worked out that your circuit does not work as a missing pulse detector.?

Did you measure the Vcap voltage as I suggested.?
E

Update.
Do you want me to make the required changes to your circuit.?

 

On my model, the minute I add that R7 connection from the trigger to positive rail, that’s what happens.

Are you sure your transistor model hasn't been inadvertently replaced by an NPN one?