# First Project: Voltage Indicator

Discussion in 'The Projects Forum' started by marx, Oct 4, 2009.

1. ### marx Thread Starter Member

Oct 4, 2009
64
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Hey Guys first time posting, haven't had much of a detailed look through this forum but from from the little I have seen, its pretty obvious that there is a wealth of information here.

I have a background in Civil Engineering but I have just started picking up some Electrical Engineering papers as I find this field so much more interesting (I wish I figured that out sooner)

Anyway I'm relatively fresh to Electronics and I was hoping for a bit of guidance for a project I have chosen as part of a paper I'm am doing. I have just finished the theoretical part of this paper but now I have to put that into something practical.

This is what the circuit should achieve:

A circuit which lights a LED when a voltage is above 14 volts and flashes the LED (at about 1Hz) below 10 volts. The circuit should also continually sound a buzzer when it go out of this range in either direction.

I've only just started putting some thoughts together today so it might be a bit premature posting this but if you have any pointers as to what I should be focusing on to get this project started that would be appreciated.

Marx

2. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
What do you need the LED to do when the voltage is between 10V and 14V?

hgmjr

3. ### marx Thread Starter Member

Oct 4, 2009
64
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The LED will be off when the voltage is inside the 10-14 V range.

4. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
Have you given any thought to what you would use to power this circuit?

hgmjr

5. ### hobbyist AAC Fanatic!

Aug 10, 2008
885
85
to clarify what you wrote,

The buzzer and the flashing of the LED, come on only when the voltage is below, 10 v. and, above 14v. and in between these two thresholds, the circuit remains off?

6. ### marx Thread Starter Member

Oct 4, 2009
64
0
Probably a couple of 9 or 6 volt batteries at this stage.

Will eventually get a decent power supply with multiple outputs but probably won't get around to doing that before this project needs to be finished.

Above the 14V the LED is lit (no flashing) and buzzer is sounding.

Below the 10V the LED is lit (Flashing 1hz) and the buzzer is sounding.

And yes in between those two thresholds the circuit will be off.

7. ### tibbles Active Member

Jun 27, 2008
249
3
a couple of comparators 1 off at 10 volt, 1 on at 14v into an 2 or gate?

8. ### Wendy Moderator

Mar 24, 2008
21,424
2,951
How precision do you need these voltages? I think it can be done wth one battery easy thinking about it, any voltage. So pick your prefered battery.

I'm one of the guys who can't help themselves around here, I'll see what I can draw up. It could take as long as a week though, got a full schedule Tue-Thur. I'm a youth advisor for a boys club called DeMolay, and they've over booked me. But is a good cause.

It occurs to me you may just want some hints after rereading the post. How much help do you want? I don't want to take away the fun of it.

The first thing this will need to do is a voltage divider, to get the sensed voltage to a lower range (for the battery basically), then use a device called a comparitor. A LM339 has 4 of them in one package, they are a cross between a digital gate and an analog circuit.

Last edited: Oct 5, 2009
9. ### tibbles Active Member

Jun 27, 2008
249
3
hi bill
i know this is not the place and apologies to marx, but have you always lived in the states? its just that your name is common, in the nicest sense of the word ,where i live in the north of england.

10. ### tibbles Active Member

Jun 27, 2008
249
3
marx
flashing leds are readily availble now i think at 1 hz and not badly priced that should save a bit of time

11. ### Wendy Moderator

Mar 24, 2008
21,424
2,951
I've visited the town of Marsden, if that's what you mean, when my dad was stationed in Lakenheath. I must have been around 7 at the time.

We're American, several generations back, with a smattering of Rose and Murphy besides.

The design currently in my head was going to use the 555 as the LED driver, both for the flasher and the solid indicator. I'll wait for the OP to get back with us.

12. ### tibbles Active Member

Jun 27, 2008
249
3
i live about 5 miles from MARSDEN they THEY USE IT A LOTTHEY USE IT A LOT

13. ### tibbles Active Member

Jun 27, 2008
249
3
sorry ignore that, must have hit the post button
i live about 5 miles from marsden ,they use it a lot on the tv comedy last of the summer wine

14. ### marx Thread Starter Member

Oct 4, 2009
64
0
Hey Bill, thanks so much for your offer to help.

This is very much a learning exercise for me and its also worth 20% of the paper and I don't want those marks to be handed to me. So if you have the time to explain the circuit that you have in mind then that's cool but if you don't just some pointers will be great.

I'd like to get the voltages as accurate as possible, as we will be marked on quality, accuracy, theory and test results.

Regarding the flashing LED, I'd probably be keen to get an better understanding of how to make a standard LED flash.

15. ### marx Thread Starter Member

Oct 4, 2009
64
0
In terms of stages, here are my thoughts so far.

Any thoughts? don't mind being told that its completely wrong.

Last edited: Oct 5, 2009
16. ### tibbles Active Member

Jun 27, 2008
249
3
sorry its a bit crude, its bedtime in the uk

bill will no doubt put us right

if you need more detail let us know

the funny looking bit in the middle is an or gate to bring the 2 outputs togrther. may not be nessesary.
you may get away with 1 555 but 2 would be better

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17. ### tibbles Active Member

Jun 27, 2008
249
3
marx now ive woke up your drawing makes more sense than mine, i was trying to avoid too much duplication but you may need 2 comparators to accomodate the dead band

18. ### tibbles Active Member

Jun 27, 2008
249
3
marx
just a thought ,are you able to breadboard this project? if so you can assemble the comparator section and set the trigger points etc before you move on to the output circuit/s.
just temporarily rig up an led with a 1k resistor to monitor the outputs

19. ### marx Thread Starter Member

Oct 4, 2009
64
0
Yep this will be done on a breadboard.

The breadboard I have has 640 terminal holes which I'm thinking should be ample.

20. ### marx Thread Starter Member

Oct 4, 2009
64
0
We were given a list of components we should get for the course. I've purchased everything that is on the following list except resistors, capacitors so I will be looking to use these components.