voltage divider - Electronic Circuits Projects Diagrams Free

AtomSoft · 10th August 2009, 07:43 PM

How do i calculate 2 resistors value for dividing voltage?

Like i have a 3.3v supply but need it to be 2.5v-3v.

Whats the formula or how would i do this in ohms law?

blueroomelectronics · 10th August 2009, 07:47 PM

If you're using it as a voltage reference you'll find it may vary under load. A simple shunt regulator like the common TL431 is a very good voltage reference.

Else here's a voltage / resistor divider calculator link.
BeyondTTL Resistor Voltage Divider Calculator

AtomSoft · 10th August 2009, 09:28 PM

thanks bill

rayslab · 10th August 2009, 09:31 PM

The ratio of R2/(R1+R2).
Input goes to R1, output comes from junction of R1 and R2.
R2 also goes to ground. Input is ground to R1.
Output is ACROSS R2, to gnd.
Multiply the input voltage by this ratio.

If the load, which attatches to R1-R2 junction is known in Ohms, include it with R2, say R2'=the parallel combo of R2 and the load.
The ratio is then R2'÷(R1+R2'), multiply this loaded divider by the input voltage.

You can choose the lowest value of R's that your source can furnish current to, reducing load resistor effect. Since the R2 is parallel with the load, the smaller R2 the closer the combo is to R2.

AtomSoft · 11th August 2009, 12:46 AM

ok smart people i have a 12v battery nice and small its called a type N.
12V Alkaline Battery (2-Pack ) - RadioShack.com

Can i use a 5.1 Zener to drop the voltage for usage with a pic? if so how? I never used Zener before...

birdman0_o · 11th August 2009, 12:55 AM

Power Supplies

Give that a try

AtomSoft · 11th August 2009, 01:16 AM

PERFECT!!! Thanks!

kchriste · 11th August 2009, 03:36 AM

A 78L05 or a low power LDO would be better. That battery only has 40 mah. It won't last long!

AtomSoft · 11th August 2009, 10:30 AM

I might just take 2-3 AA batteries .. rechargable with a nice 2500mAH.. which would mean this would last about 125 hours on 1 full charge.

Thats about 1 charge a month... How many times can one charge a battery before it dies?

Hero999 · 11th August 2009, 11:04 AM

Yes, two AA cells will last much linger than that tiny 12V battery.

If I remember rightly a NiMH cell can survive 500 cycles after which its capacity is reduced to 80% of the original.

AtomSoft · 11th August 2009, 12:37 PM

awesome!!! The size is what bothers me but heh its its more efficient then i might as well use em...

Saves money too!

MrAl · 11th August 2009, 01:34 PM

Hi,

Also, if a 12v battery is used to power a 5v device with a zener or other
linear regulator there is a lot of battery power wasted as heat. If a
switching regulator was used instead, two times the run time could be had.
Instead of (say) 1 hour, it would run 2 hours.
This is only true when the input voltage (12v) is way above the output (5v).
With three AA cells, that's only 4.5v and you could run the PIC directly
without any regulator (5v PICs) unless you need to do voltage measuring AD
converts which then you also need a stable voltage reference.
If you are doing ratiometric converts you dont need a voltage reference though.

One additional little note:
If you use the sleep mode you can wake the chip up once in a while to do
a measurement. The battery can last for years this way.

AtomSoft · 11th August 2009, 01:48 PM

cool.... How can i put a pic into sleep mode? Never tried.. also how do i wake it up?

AtomSoft · 11th August 2009, 01:51 PM

By the way its for a small sound toy i made my son. it has 5 buttons all to play different tones. I chose the ones he like the most..

Im going to get a little case made for it also.

He first heard the noise when i was testing the buzzer on my LPC and tried to rob me of it heh

So i decided to make the same thing with my PIC chips and he like it but im not going to hand him a PCB with some batteries lol hence the case. i will test out :

Polycase - Plastic Electronic Enclosures

site and see if their service is good.

q5101997 · 11th August 2009, 03:00 PM

LDO (low dropout voltage) regulators are ideal for battery powered equipment where every volt counts. If the difference between the input (battery) and output (load) voltage is greater than 0.2V, then the regulator will disipate more power. If the I/P to O/P difference is large (ie battery = 12V, load = 3.3V), then the power dissipation will be like a standard 7805. LDO regulators are designed to run on small voltage differences. For a 3 x 1.2V AAA NiCa battery pack that starts at 4V fully charged and drops to 3.5V when discharged, critical circuits need to maintain a nice constant voltage. In this case, the load voltage would be govorned by the regulator at 3.3V while the battery voltage drops to 3.5V (3.3 = 3.5 - 0.2). Heres a 0.2V minimum dropout, 3.3V @ 100mA LDO regulator to look at.

Regs Q

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10th August 2009, 07:43 PM	#1
AtomSoft	voltage divider How do i calculate 2 resistors value for dividing voltage? Like i have a 3.3v supply but need it to be 2.5v-3v. Whats the formula or how would i do this in ohms law? __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

10th August 2009, 07:47 PM	#2
blueroomelectronics	If you're using it as a voltage reference you'll find it may vary under load. A simple shunt regulator like the common TL431 is a very good voltage reference. Else here's a voltage / resistor divider calculator link. BeyondTTL Resistor Voltage Divider Calculator __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

10th August 2009, 09:28 PM	#3
AtomSoft	thanks bill __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

10th August 2009, 09:31 PM	#4
rayslab	The ratio of R2/(R1+R2). Input goes to R1, output comes from junction of R1 and R2. R2 also goes to ground. Input is ground to R1. Output is ACROSS R2, to gnd. Multiply the input voltage by this ratio. If the load, which attatches to R1-R2 junction is known in Ohms, include it with R2, say R2'=the parallel combo of R2 and the load. The ratio is then R2'÷(R1+R2'), multiply this loaded divider by the input voltage. You can choose the lowest value of R's that your source can furnish current to, reducing load resistor effect. Since the R2 is parallel with the load, the smaller R2 the closer the combo is to R2.

11th August 2009, 12:46 AM	#5
AtomSoft	ok smart people i have a 12v battery nice and small its called a type N. 12V Alkaline Battery (2-Pack ) - RadioShack.com Can i use a 5.1 Zener to drop the voltage for usage with a pic? if so how? I never used Zener before... __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

11th August 2009, 12:55 AM	#6
birdman0_o	Power Supplies Give that a try __________________ Mike My website: www.ElectroBird.net Last edited by birdman0_o; 11th August 2009 at 12:56 AM.

11th August 2009, 01:16 AM	#7
AtomSoft	PERFECT!!! Thanks! __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

11th August 2009, 03:36 AM	#8
kchriste	A 78L05 or a low power LDO would be better. That battery only has 40 mah. It won't last long! __________________ Inside every little problem, is a big problem trying to get out.

11th August 2009, 10:30 AM	#9
AtomSoft	I might just take 2-3 AA batteries .. rechargable with a nice 2500mAH.. which would mean this would last about 125 hours on 1 full charge. Thats about 1 charge a month... How many times can one charge a battery before it dies? __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics Last edited by AtomSoft; 11th August 2009 at 10:38 AM.

11th August 2009, 11:04 AM	#10
Hero999	Yes, two AA cells will last much linger than that tiny 12V battery. If I remember rightly a NiMH cell can survive 500 cycles after which its capacity is reduced to 80% of the original. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

11th August 2009, 12:37 PM	#11
AtomSoft	awesome!!! The size is what bothers me but heh its its more efficient then i might as well use em... Saves money too! __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

11th August 2009, 01:34 PM	#12
MrAl	Hi, Also, if a 12v battery is used to power a 5v device with a zener or other linear regulator there is a lot of battery power wasted as heat. If a switching regulator was used instead, two times the run time could be had. Instead of (say) 1 hour, it would run 2 hours. This is only true when the input voltage (12v) is way above the output (5v). With three AA cells, that's only 4.5v and you could run the PIC directly without any regulator (5v PICs) unless you need to do voltage measuring AD converts which then you also need a stable voltage reference. If you are doing ratiometric converts you dont need a voltage reference though. One additional little note: If you use the sleep mode you can wake the chip up once in a while to do a measurement. The battery can last for years this way.

11th August 2009, 01:48 PM	#13
AtomSoft	cool.... How can i put a pic into sleep mode? Never tried.. also how do i wake it up? __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics

11th August 2009, 01:51 PM	#14
AtomSoft	By the way its for a small sound toy i made my son. it has 5 buttons all to play different tones. I chose the ones he like the most.. Im going to get a little case made for it also. He first heard the noise when i was testing the buzzer on my LPC and tried to rob me of it heh So i decided to make the same thing with my PIC chips and he like it but im not going to hand him a PCB with some batteries lol hence the case. i will test out : Polycase - Plastic Electronic Enclosures site and see if their service is good. __________________ AtomSofts eBay Store AtomSoftTech: C18 TIPS & TRICKS v9 PDF Nokia 6100 Driver/Software My Name: Jason Lopez http://atomsofttech.info/ \| My YouTube Videos! My Favorite Store: dipmicro Electronics