How to Arrange 7-8 LEDs for RF Signal Strength Indication—Series or Parallel?

Hello,

We am working on a project related to detect the RF signal. upon detection an LED will be ON and buzzer will sounds. the glow of the led becomes more when the signals are detected from near by, and dims as we move away from the source.

we wish to use several LED(about 7-8) and when the signal is strong all LEDs glow, as the signals fades the no. of glowing LEDs also decreases.

Now we are confused about the arrangement of LEDs, we think that the LEDs should connected in series, and it will work as desired.

Please give your suggestion.

thanks and regards

If you really want to use the brightness change of the LED or LEDs as a signal-strength indicator, the current through the LED(s) will change their brightness in response. More current = more brightness.

Many radio receiver chips have some kind of Received Signal Strength Indicator (RSSI) output that produces a voltage proportional to signal strength. This can be used to drive one or more LEDs with the appropriate amplifier (since the RSSI output probably can't supply more than a couple of mA of current, and LEDs typically need 5-20 mA to glow brightly).

However, if you want to use several LEDs to indicate strength, you might want to use something like a LM3914 LED driver IC, which will light up to 10 LEDs in sequence when fed a voltage. This is an easy and popular method, and performs better than simply varying the glow of a light.

Yes, if you string similar LEDs in series, they will ALL grow brighter or dimmer at the same rate. But, it sounds like what you what is more like a "Bar Graph" effect. Marks solution is probably the best (use an LM3914).

BUT, if you want a cheap and dirty solution, then how about DISSIMILAR LEDs in series. For example, a Red LED in series with a Yellow LED in series with a GREEN LED. Each has a progressively higher forward voltage and thus each will dim at different rates--the Red will glow the longest, and the Green the shortest.

AND, of course, provide proper current limiting to that series string (of LEDs).

And, consider this. If you use an LM3914, you won't get an "analog" dimming effect, unless you modulate the current through the LEDs in the LM3914 circuit. Otherwise, you'll need to have an ADDITIONAL LED that indicates the level via brightness.

Hi Steve or should i say good evening

He could also use a PIC micro with adc with led’s coupled to a port if he wants pwm then he can do this as well using a led driver on i2c bus coupled to the pic or arduino

More modern up to date method of doing this now Yes that answer will work but in view of ever changing technology I’m suggesting that we try and move people forward into modern day technological approaches so that they are prepared for changes that lay ahead , many of them there are too these days

Here is another method and that is to drive an led coupled resistor assemby (led operated LDR) such as used these days to operate volume controls and analogue amplifiers I dont know if you have seen these but they are now regulary used on gain controls Opto coupled volume controls all done with optoelectronics now

Here is some code without adc but used on a pic micro which i used to measure light intensity

Written In pic basic I was expermineting at the time with automatic light sensing for vehicles but have put this to one side he could use this adapted for what he wants to do

[code]
'****************************************************************
'* Name : LightMeter.BAS *
'* Author : MD Harrington *
'* Notice : Copyright (c) 2013 @www.harrington.force9.co.uk *
'* : All Rights Reserved *
'* Date : 14/04/2013 *
'* Version : 1.0 *
'* Notes : *
'* : *
'****************************************************************

Device = 16F84A
Config RC_OSC , WDT_OFF , PWRTE_OFF, CP_OFF
Xtal = 4
On_Interrupt GoTo INTPROC

' Variable declaration
Dim FLAGS As Byte


Symbol T0IE = INTCON.5 ' TMR0 Overflow Interrupt Enable
Symbol T0IF = INTCON.2 ' TMR0 Overflow Interrupt Flag
Symbol GIE = INTCON.7 ' Global Interrupt Enable
Symbol PS0 = OPTION_REG.0 ' Prescaler ratio bit-0
Symbol PS1 = OPTION_REG.1 ' Prescaler ratio bit-1
Symbol PS2 = OPTION_REG.2 ' Prescaler ratio bit-2
Symbol PSA = OPTION_REG.3 ' Prescaler Assignment (1=assigned to WDT 0=assigned to oscillator)
Symbol T0CS = OPTION_REG.5 ' Timer0 Clock Source Select (0=Internal clock 1=External PORTA.4)
Symbol RPBU = OPTION_REG.7 ' weak pull ups clearing set these to on
Symbol LIGHTFLAG = FLAGS.0 ' Flag for detecting if we should check light intensity



Dim LIGHTVAR As Word
Dim REPEATS As Byte
Dim PORTVAL As Byte
Dim TMRCOUNT As Byte
Dim NEWVAL As Byte
Dim CURVAL As Byte

GoTo Over_Int


'--------------------------------------------------------------------------------------

' interrupt procedure starts here


INTPROC:
Context Save


If TMRCOUNT >= 0 And TMRCOUNT < 30 Then
PORTB.7 = 1
End If

If TMRCOUNT >= 30 And TMRCOUNT< 60 Then
PORTB.7 = 0
End If

If TMRCOUNT = 60 Then
TMRCOUNT = 0
End If

TMRCOUNT = TMRCOUNT + 1

T0IF = 0 ' clear the timer overflow flag
T0IE = 0

TMR0 = 0 ' clear the timer


Context Restore
Retfie
' this is the end of the interrupt service routine
' ------------------------------------------------------------------------------------



Over_Int:
START:
GoSub INIT: ' call init this is the procedure that sets up ports etc


MAIN:




High PORTA.2



LIGHTVAR = RCIn PORTA.2, High ' read the value from the LDR
' store this in light value
GIE = 0 ' disable Global interupt here
T0IF = 0 ' clear the timer overflow flag
TMR0 =0 ' Clear the timer







PORTVAL = LIGHTVAR.HighByte

' Assign to NEWVAL
If PORTVAL > 0 And NEWVAL != PORTVAL Then
NEWVAL = PORTVAL
End If

If NEWVAL = 0 Then
CURVAL = 0

Else If NEWVAL >= 1 And NEWVAL < 3 Then
CURVAL = 1

Else If NEWVAL >= 3 And NEWVAL < 5 Then
CURVAL = 3

Else If NEWVAL >= 5 And NEWVAL < 8 Then
CURVAL = 7

Else If NEWVAL >= 8 And NEWVAL < 11 Then
CURVAL = 15

Else If NEWVAL >= 10 And NEWVAL < 14 Then
CURVAL = 31

Else If NEWVAL >= 14 And NEWVAL < 20 Then
CURVAL = 63

Else If NEWVAL >= 20 And NEWVAL < 30 Then
CURVAL = 127


End If

DelayUS 50
PORTB = CURVAL


T0IF = 0






GoTo MAIN




INIT:
All_Digital = true ' turn off analogue module



' clear all interrupt flags etc

Clear INTCON
Clear PORTB ' make shure no output on port b
Clear PORTA ' make shure no output on port a
Clear PORTVAL ' Clear PORTVAL variable
Clear OPTION_REG ' Clear option register

'clear all the variables

CURVAL =$00
NEWVAL =$00
LIGHTVAR = $00
LIGHTFLAG = 0
TMRCOUNT = $00

TRISB = $00 ' make all port B output



' Set up the prescaler
' 15 times per second prescaler setting so in 30 counts 2s econds will elapse
' 15 counts 1 second has elapsed

PS0 = 1
PS1 = 1
PS2 = 0
PSA = 0


' start interrupt procedure

RPBU = 0
TMR0 = $00

Return



[/code]

Im busy right now but this is easily altered for adc input he may need to simply add an opamp to give hime the voltage swing up to 5volts for the input This howver works quite well with RC in on port measuting charge discharge time So pretty easy to implement

Just another suggestion for you different approacch to this

What you need to take into consideration is very soon the LM3914 will be obsolete you wont be able to buy them This is why Pic micro with adc and arduino or atmel if you like "The digital era "

Good point!

This, while true, makes an old analog guy like me rather sad. It doesn't seem efficient to have to write a couple hundred lines of code if all you have to do is light a few LEDs, when that function had been contained in one simple IC. I know the Pic, etc., can do vastly MORE of course, but sometimes you only need to do one simple thing.

A few years ago I had to design a circuit to take NTSC or PAL analog video and convert it to its RGB (red, green, blue) analog component signals. In the 1980s this was accomplished with one 28 pin IC and a handful of parts, and one reasonably-competent engineer could have it working in a few days. 25 years later it took a microprocessor and two 64-pin digital chips to do the same job, plus MORE support parts and twice the power, never mind the week or two of programming and debugging. I'm not sure this is progress!

You kids stay offa my lawn!

Think about it a little bit more Mark

What the problem we are all facing

Throw way age So whats the answer Think Mark I know exactly what your saying and I also know there is much truth in what you say but now think re usable and think not out of work think extra work they have created and also think Why not simply reprogram one micro to do many jobs thus saving the PCB , also saving chips also creating more jobs

Whats the answer program a chip to do the same thing

What else springs to mind here

How about this for an example : You phone up a manuifacturer and ak for a specific chip " , whats theier normal answer , " We havent got that in stock " , which is true most of the time , Think also your client is sitting in anoter country and cant get this to work , whats the answer send him the hex code He plugs his unit into the network the units sends out a message and bing within five seconds after fitting one blank micro his unit is up and running again Wheres the stock control gone Its diminished ( No more Hard work ) Come on boys think !! Wakey , wakey time



Is this not far easier

Its acceptance Mark Its moving with times If we don’t point this out what’s going to happen when this all does change and their are no more analogue chips around that do this job

Do we just simply say nothing Edison long time ago produced a light bulb Today its led lighting , 12 volt systems Money saving cost effective less bills to pay

SOS may day may day officer down requesting urgent backup

http://www.dailymail.co.uk/news/article-23548...emale-colleague-injured-try-evict-tenant.html

http://www.dailymail.co.uk/news/article-23310...ered-soldier-Lee-Rigby-visit-street-died.html

http://www.guardian.co.uk/uk/london-riots

(Today Mark Today Not yesterdays news Todays news In the UK ) did they intercept radio communications is there a problem out there I think so dont you

http://www.huffingtonpost.co.uk/2013/04/10/brixton-riots-1981-anniversary_n_3058292.html

http://www.telegraph.co.uk/news/uknews/crime/...akelock-murder-new-charge-after-27-years.html

Think one more stage I need to get an armed services units radio reprogrammed in a hurry, its an emergency They are out in a deadly combat zone He / She hasn’t got time to try and fit new Ics They under heavy fire The enemy have intercepted their radio units

What’s the answer Connect on this channel on a service channel maybe a mobile phone, satelight uplink what do I do ask him / her to do , plug the radio coms unit into the phone place the unit into PRG mode and I do what Mark send it a hex file over the air using channel hopping and recode the radios( multiple) in 5 milliseconds The difference between saving a platoon and not saving that platoon The difference between saving lives and not saving lives



Think further than this Mark Think how many parts they would have to carry all the time instead of one micro pluggable exchangeable easily connected easily reprogammed to suite a situation

Whats Up Mark ( think Think )

Thats Future of electronics my friend

Why do we need hackers aaah To see if the sytems can be penetrated Yes !!! Flipping well done at last

Think Positive Mark "Not negative" , all things happen for a reason

Its not a game anymore Mark ITS WAR !!!

Me,too!

But, on the bright side, using a uController means you can make it do what you want it to do (i.e. not limited to the implementation of the specialized IC). Can't tell you how many times I've needed the output of the 555 timer to be inverted. In that case I use a 556 and use the second timer as an inverter ('cuz I also needed the drive capability of a 555 output =) But, with a PIC, I can just program the output (of course, this is probably a bad example, because there ain't no PIC that can drive like the 555 can!

:P

Hi Mark.
I must confess that software and microprocessors reallly scare me. I have always used hardware solutions only. I failed a microprocessor course, I think because lecturer was good with micros but bad at teaching. I can clearly see benefits particularly in DSP, as I am always interested in improving HF radio in strong QRM and QRN situations. Do you know of any literature which on its own can help? The other thing is that making a one of design in micros (as I understand) is very costy in that it cannot be done in a personal lab (like mine) I am quite dedicated and have a good DSO and an Agilent (new) spec ann with all the extras, I alsso am a prolific inventor especiallr in RF and have been for 50 yrs. i.e. I am a hard boiled veteran t RF dsign ha ha.

Hi Rodney

http://www.mybookezz.org/c-programming-for-pic-microcontrollers-tutorials-1142/

Tons and tons of literature for you on this page free for download and then go to Maplins , or Rs Components Or Farnel or Proton Basic Buy yourself a development kit from the above good prices at the moment

Compilers are often free
Theres Code blocks , SDCC open scource , Eclipse etc , plus download ver 8.5 IDE from Microchip , you will need this

If you need extra help yell see what I can do for you

http://www.sourceboost.com


Other tuts you can follow

Start here
http://www.talkingelectronics.com/projects/Elektor/TalkAboutMicros/TalkAboutMicros.html

http://www.8051projects.net/t5905/pic-microco...m-pic16f877-using-visual-basic-in-digital.htm

Also follow these tutorials as well
http://www.lammertbies.nl/comm/index.html
Another good site
http://www.lvr.com/parport.htm#Basics

Pic Input Output
http://www.piclist.com/techref/ios.htm

Working with binary numbers hex and so forth
http://www.bearcave.com/software/divide.htm


Working with fixed point maths
http://www.best-microcontroller-projects.com/fixed-point.html

Advanced topics
http://www.dattalo.com/technical/theory/dtmf.html
http://www.eix.co.uk/Ethernet/WWarticle.htm

Discussion Groups forums etc
http://www.electro-tech-online.com/


With reference o RF and Amatuer radio more up your street

One google search reveals all
interfacing+pic+micro+to+amatuer+radio

Start here
1: http://www.qsl.net/dl4yhf/
2: http://www.westmountainradio.com/content.php?page=pic_resources
3: http://wb9kzy.com/projects.htm
4: http://www.arrl.org/ic-programming-and-amateur-radio-projects
5:http://terraceamateurradio.net/ClubProjects/Microcontroller%20for%20a%20simple%20repeater.htm
6:http://www.eee.bham.ac.uk/joness/satproj.htm
7:http://radcomms.net/Jabra_A210.html

See below for download as well

Tons of info out there Rodney "take your pic lol"

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Informative Post.