[PSU WITH LCD VOLTMETER--TROUBLE!!]

audioguru you a God!!!!

Thank you.

Ill post again after i try this.

[PSU WITH LCD VOLTMETER--TROUBLE!!]

Thanks audioguru,

ill try this when i find the time, but i have a little problem..

My LCD need at least 8volt supply . is there any IC that inverts this range of voltages?

[PSU WITH LCD VOLTMETER--TROUBLE!!]

Stath,
I am not clear why you are using an adjustable regulator, then you have an additional adjustment pot after the regulator.

The second pot (POT2) is not part of the supply cct; it is part of the measuring cct.
The resistence of the voltage divider (680kohms +the POT2) is very high so i think that its load is negligible .

If you must have an isolated ground, you can use a higher voltage regulator and lift the ground up from common with a resistor.

I've tried this with a simpler way ; i lifted the measuring ground from common by using a resistor. Same, bad resutls!

I have also seen a post from ante where he coils a piece of wire and puts it on the transformer to make an isolated tap. Then rectifies it as an isolted small voltage supply.

This is interesting!

A Question...
?? Do transformers can use for step-down in DC source as their are used in AC sources?

Thanks MP

audioguru,

I cant get the idea of using an inverter. what i can acheive with this?

[Constant current source for high brightness LEDs]

Hi,

You can use the cct below if fits your needs.

R1  (1kohms is fine) controls the current, so you can control the brightness

R2 must be selected according to the specs or the LED, to prodect it ( may not needed)

[Mini project (Help me)]

Hello,

r-care, my mini-project in univercity was a "4-band audio equalizer" and i used over 8 OPAMP's to do it. i studed very hard i feel able to help u.

just give info about:

the order of the filter (1st, 2nd,....,6th)?

is it a band-pass filter?

do you have to use Bjt's or is it optional?

what about gain?


Thanks.

[Exaust Fans for Entertainment Center]

Hello,

Just to add my idea,

I angree with Ante; you dont need to control them. Just set them up at a constant speed!

Also have in mind ( if not already), use one for inlet and one for outlet.

[counting device]

Hi,

i have to say that i had the same idea few months ago.

A device that counts how many people enters a single door; e.g. a restaurant.

I was thinking of using an optocouple or ir emmiter and transmiter. when the ir light that the emmiter receives is interrupted by a human body, it produce a reset of a flip-flop or a clock and produce an increment on a counter.

counter`s outputs update a BCD decoder state .

This is an overview of my idea...

i dont know ecxactly what IC`s are suitable for this but you have to make a little search on logics gates - counters, encoders- decoders, 7-segment display.

if you have Multisim 7 software may be very useful

[PSU WITH LCD VOLTMETER--TROUBLE!!]

HI.....
MP, plase take a good look , the sample for the measuring point is taken on the middle point of a voltage divider of >680kohms

And i remind you that this proplem is solved then i supply the voltmeter circuit from a 9volts battery... This is the mystirious fact for me.

??> The datasheet of the LCD panel says:
   
        " CAUTION! SUPPLY GROUND MUST BE ISOLATED FROM MEASURING GROUND"

That's why there is no problem when i supply the cct from a battery; battery is a separate source from my cct!!!

Thanks to MP, and audioguru.

[trasformerless powersupply]

Bruce,

Just an advise.....

High voltages such an 220 and 110 volts are DANGEROUS!!

Transformers povide isolation from the mains power so,

my opinion is that you must always use transformers when dealing with high voltages...
Thanks.

[PSU WITH LCD VOLTMETER--TROUBLE!!]

Thanks Very much MP!!

Here is the diagram...

[PSU WITH LCD VOLTMETER--TROUBLE!!]

Hello to every one!! this is the first time firsttime im writting to forum.

i found this website the most usefull for me since im a student in elect. eng.

i hope that someone will help me with a problem i had building a LAB P.S.E

I used a power supply from an old destroyed printer. I did some measurements and it was working JUST FINE!

OUTPUT 1: 24v @ 2.5A
OUTPUT 2: 5v

So, i decided to build a subcircuit using an LM317 regulator to adjust the 24v output, and a volt meter using an LCD. I was 100% sure that it will work!

I built it, power it up, and .......... The voltmeter was indicating INFINITE VOLTS!
I found out