8 replies to this topic

[Steven Behnke]

Which components should I buy for a brand new netdruino? Like, what kind of resistors and LEDs should I get? I know 3.3 volt lcds are recommended, but how does the the lower voltage affect the other components found in arduino tutorials?

[Chris Walker]

For LEDs and the like, you should be fine as-is. If you have the chance to buy a 3.3V version of a component rather than a 5V version of the component, you'll generally want to do so. The most important case is with communication protocols (SPI, I2C, UARTs, etc.) Many components can take either 3.3V or 5V, but some are more particular. If in doubt, feel free to ask questions about particular parts here... There are a lot of people with electronics experience in the community. Chris

[Flores]

For LEDs and the like, you should be fine as-is. If you have the chance to buy a 3.3V version of a component rather than a 5V version of the component, you'll generally want to do so.

The most important case is with communication protocols (SPI, I2C, UARTs, etc.) Many components can take either 3.3V or 5V, but some are more particular.

If in doubt, feel free to ask questions about particular parts here... There are a lot of people with electronics experience in the community.

Chris

Isn't a 5mm led using about 30mA, so too much for directly to the digital outs which can supply only 16mA?
Shouldn't we use a driver of some sort ?

[CW2]

Isn't a 5mm led using about 30mA, so too much for directly to the digital outs which can supply only 16mA?Shouldn't we use a driver of some sort ?

Yes. Unlike AVRs, Netduino cannot drive 20~30 mA LEDs directly. Depending on your intended usage, it may be sufficient to drive the LED with only 15 mA, it will be a bit dimmer, or you can use LEDs for smaller current (2 - 10 mA).

Please note Netduino has only three pins that can draw 16 mA (D3, D4, D7), analog pins can draw only 2 mA in digital mode, the rest of pins can draw only 8 mA.

[Flores]

Yes. Unlike AVRs, Netduino cannot drive 20~30 mA LEDs directly. Depending on your intended usage, it may be sufficient to drive the LED with only 15 mA, it will be a bit dimmer, or you can use LEDs for smaller current (2 - 10 mA).

Please note Netduino has only three pins that can draw 16 mA (D3, D4, D7), analog pins can draw only 2 mA in digital mode, the rest of pins can draw only 8 mA.

Okay. What would be the simplest schematic and/or component to use, if I want to make sure I don't wreck my netduino connecting the outputs to stuff drawing more than those mA's?

Thanks.

[CW2]

Okay. What would be the simplest schematic and/or component to use, if I want to make sure I don't wreck my netduino connecting the outputs to stuff drawing more than those mA's?

It depends on the number of LEDs and their wiring - for example, for a single 'indicator' LED I would just add current limiting resistor, a few LEDs can be driven by separate transistors, for bigger amount and complex circuits an integrated Darlington array, power shift register or specialized/dedicated LED driver IC would be more suitable. Could you provide more details on what exactly you would need?

[Flores]

I just want to connect a number of 50mA leds. Will any transistor do then? And does something like 8 transistors in a IC package exist, so I can connect them to all my outputs and connect 8 leds?

[CW2]

I just want to connect a number of 50mA leds. Will any transistor do then? And does something like 8 transistors in a IC package exist, so I can connect them to all my outputs and connect 8 leds?

Yes, any general purpose transistor like BC54x (Ic = 100 mA) or 2N4401 (Ic = 600 mA) will be fine. I often use ULN280x Darlington array (Ic = 500 mA) or serial-in/parallel-out shift register 74HC595 (20-35 mA, various derivatives) to drive multiple LEDs (matrices).

However, there are still a few other things to consider, for example 8*50 mA = 400 mA, which is close to the limit a USB port can provide (500 mA) and I think I have seen in the firmware source code that Netduino is configured at only 280 mA (have to verify this), so you may not be able to power the Netduino and LEDs from the USB port, an external power supply would be required. And, if you are driving the LEDs by PWM or multiplexing, the peak current can be significantly higher, so you'd need to account for it when selecting the components.

This is why I (annoyingly) ask for details, in my experience "connecting a LED" can mean anything from multiplexed 16*16*16 cube to 20 W RGB power LED...

[Flores]

Yes, any general purpose transistor like BC54x (Ic = 100 mA) or 2N4401 (Ic = 600 mA) will be fine. I often use ULN280x Darlington array (Ic = 500 mA) or serial-in/parallel-out shift register 74HC595 (20-35 mA, various derivatives) to drive multiple LEDs (matrices).

However, there are still a few other things to consider, for example 8*50 mA = 400 mA, which is close to the limit a USB port can provide (500 mA) and I think I have seen in the firmware source code that Netduino is configured at only 280 mA (have to verify this), so you may not be able to power the Netduino and LEDs from the USB port, an external power supply would be required. And, if you are driving the LEDs by PWM or multiplexing, the peak current can be significantly higher, so you'd need to account for it when selecting the components.

This is why I (annoyingly) ask for details, in my experience "connecting a LED" can mean anything from multiplexed 16*16*16 cube to 20 W RGB power LED...

Just for playing around and testing. Ordered myself a ULN2804. Thanks