Is it a power supply that's giving you 10V or a wall wart?·
Just note that an unloaded wall wart will have a higher voltage than what's printed on it for specs.· You need to connect circuitry (a rated lamp would work) to bring it under proper load and measure it properly.· It's akin to wave jumping in boats.· The boat is going at 40mph @ 2500RPM...well, as soon as you launch off that first wave on the wake, you go airborne and the propellor is no longer under load so the RPM's go WAY up (redlining if you're unlucky!).· This is the best I have for an anology.
Anyhow, I'll assume you are looking to run a stamp.· If you're only after the stamp to be powered with minimal circuitry (no add-ons) then you're looking at about 10mA.· (I don't have the stamp specs in front of me, but I think that'd be sufficient).·
With 10Volts as your main supply, you want it halved...so you need a voltage divider consisting of 2 resistors of the same value.· This will half the supply....to keep about 10mA of current you'll want to use 2 500ohm resistors.
here's the Calculation:· E=IR;· R = E/I = 10/0.01 = 1000ohms.· This is the total divider resistance needed for the current.· Now, divide this by 2 (500ohms) and you got your resistors.
The best resistor for this is called a "voltage regulator". It is a resistor that uses feedback to adjust its resistance to exactly the correct value to get 5 volts output, no matter what the input voltage or output current (within limits!)
+10 volts Vin ----resistor
load
ground
I
>
5 = 10 - I*R
R = (Vin - 5) / I
R in ohms, V in volts, I in amps
mize
Posts: 15
Comments
Bean.
Just note that an unloaded wall wart will have a higher voltage than what's printed on it for specs.· You need to connect circuitry (a rated lamp would work) to bring it under proper load and measure it properly.· It's akin to wave jumping in boats.· The boat is going at 40mph @ 2500RPM...well, as soon as you launch off that first wave on the wake, you go airborne and the propellor is no longer under load so the RPM's go WAY up (redlining if you're unlucky!).· This is the best I have for an anology.
Anyhow, I'll assume you are looking to run a stamp.· If you're only after the stamp to be powered with minimal circuitry (no add-ons) then you're looking at about 10mA.· (I don't have the stamp specs in front of me, but I think that'd be sufficient).·
With 10Volts as your main supply, you want it halved...so you need a voltage divider consisting of 2 resistors of the same value.· This will half the supply....to keep about 10mA of current you'll want to use 2 500ohm resistors.
here's the Calculation:· E=IR;· R = E/I = 10/0.01 = 1000ohms.· This is the total divider resistance needed for the current.· Now, divide this by 2 (500ohms) and you got your resistors.
You just connect it like this:
+----VVV---|----VVV----<>
10V··500R··· 5V···· 500R··· Gnd
Hope that's clear enough....
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·
Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
+10 volts Vin ----resistor
load
ground
I
>
5 = 10 - I*R
R = (Vin - 5) / I
R in ohms, V in volts, I in amps
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com