Help with the limits of Basic Stamp 2 ( output current )

Hills

Hi

I just want to know if I connect 6 optocouplers ( so 6 outputs ) with the basic stamp 2, is it ok·or to much for the basic stamp 2 ( too much current ) because I don't want to damaged my basic stamp 2. For more informations about the circuitry, just see the attachment where you will see an example of one of the 6 optocouplers.

Beau Schwabe

Without knowing the forward voltage drop of the LED inside the optocoupler, it's hard to give an exact answer.

Assuming that the forward voltage drop of the LED is at least 1.4V, then the amount of current that each pin
must supply is going to be about 6.1mA.

I = ( Vsource - Vled ) / Vresistor
I = ( 5V - 1.4V ) / 590
I = 3.6V / 590
I = .0061A = 6.1mA

6.1mA X 6 optocouplers is going to be about 36.6mA total, so you are just under the 40mA maximum requirement
for sourcing current (Which is what your circuit is doing). If you are sinking current the allowed maximum is 50mA.
If you are using a BS2e, then the source/sink current limit increases to 60mA.

www.parallax.com/dl/docs/prod/stamps/web-BSM-v2.2.pdf
(See page 12)


BTW) You can measure the forward voltage drop of an LED with a DMM (Digital Multi Meter) using the "Diode Test".

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

PJAllen

I'm going to work out a "one-sheeter" of ultra-basic transistor circuits for questions/situations such as this.· The output current (source or sink) capability of the STAMP-family seems a recurrent concern.

((· I wonder why the HomeWork board is kitted with·but one transistor.· How many get put into a BoE kit?· ))

···

I have a friend for whom I've made little SIP transistor-LED circuit boards with a color-coded header, all ready to go: they just·slip into the proto-board, whip in three wires (one to V_IN, ORN;·one to V_SS, BLK; and one to the STAMP pin of choice [noparse]/noparse]P[sub]X[/sub, YEL) and no more worries.· Anyone at Parallax wants to glom onto this idea --·it's OK by me.·

With two more header pins I could work in a 4Nxx "opto", that wouldn't be inventing science.