1% or 5% resistor reuired on linistepper?

[Niggo]

Hi! I'd like to know if the 1% resistor is a must on the linistepper or 5% is good too or if there are specific resistors that must be 1% or not. Thanks !!

[NC Cams]

The required resisitance tolerance is a function of the accuracy of the resistance needed to achieve the current limit or voltage that you're trying to generate.

In a real sensitive current sense circuit, 1% would be a preferred value. When you see what a 1% tolerance does to the voltage generated by say 5 amps thru a 1k ohm resistor (+/-0.010volts), only you can determine if that is too much or OK. Is that a lot or a little??? You as the circuit designer need to decide the answer to that question.

Generally, for a pull up resistor or a base resistor for a transistor, 5% tolerance parts are quite adequate as the tolerance doesn't matter that much in that useage.

When it all shakes out, the use of 1% versus 5% tolerane resistors depends what you want and need to do with the circuit.

[Niggo]

Well I think only the linistepper designer can tell that or who bought the kit can list which resistor is 1% or 5%, but I prefer someone who describe why to use 1% , if any, so I can learn.

[NC Cams]

I just did explain why - please re-read paragraph #2 in my prior post.

The circuit designer determines the resistance tolerance needed using Ohm's law. This law states that the DC voltage drop across a resistor is a function of the resistance in ohms times the current flowing through it.

If you vary the resistance value by 1% (the tolerance) and the voltage drop for any given current will vary from the nominal resistance value by the tolerance percentage.

Now if Linistepper says to use 1% resistors, they probably designed the circuit to NEED/REQUIRE that tight of a resistor tolerance. If you are simply asking WHY to use 1% versus 5%, it is explained by the math when you analyze the circuit via Ohm's law.

If you can't find 1% resistors, simply 100% measure the resistors and select ones that are within 1% of the posted resistance value. Or buy them from Digikey or Mouser - they are not that much more costly than 5% ones.

[Niggo]

Humm my english isn't so good, sorry I understood what you said and now I'd like to have a confirm about using 1% on the linistepper or not becouse in the pictures some resistors seems 5% others (470 ohm and 390 ohm) seems different. Thanks again!

[kreutz]

Looking at the schematic at http://www.piclist.org/images/member...33/circuit.jpg there are no critical resistor values and you can use the cheaper 5% tolerance for all of them.

If you have a different schematic post it so we can check it.

[Niggo]

No, I have that one. Thanks for the answer!

[kreutz]

After looking at the Linistepper schematics I wanted to reverse-engineering how they limited the current going through the coils. It seems that the designer uses a clever trick of feeding an analog signal to the base of the power transistors, when the voltage drop on the sensing resistors plus the voltage base-emitter is higher than the analog voltage applied to the base will reverse bias the junction and will limit the current without using a chopper current limiter. In order for this trick to work reliably you will need to use 1% resistors for 150, 220, 680 and 120 ohm resistors going to the base of the transistors. All other resistors could be 5%.

I am sorry for misleading you with my prior post.

[Niggo]

No problem, thanks

[Niggo]

I have found a 392ohm 1% not 390ohm, I think it is the same, isn't it?

[NC Cams]

392 ohms is NOT mathematically equal to 390 ohms.

Electrically speaking, EITHER is well within 1% of each other and should be ELECTRICALLY interchangeable for 99.9% of most circuit requirements.

Are you looking or ELECTRICAL equivalency or MATHEMATICAL equivalency???

Either way, the answer is provided above.

[kreutz]

Look at the following tables, those are the typical standard 1% and 5% base resistor values you will find commercially. The 1 % table is supposed to include the 5% values as well.

http://eet.etec.wwu.edu/etec271/StdR...or%20values%22

For your circuit (linistepper) the 390 ohm resistors could be 5% tolerance, so 392 is OK. They are just current limiter resistors used as protection on the PIC micro-controller's input pins (they protect the parallel port output as well).