Asked — Edited

Digital Io Pull-Up Resistance

What is the resistance value of the pull up resistors on the V4 boards? I'm working on LED's for my robot before the development kits roll out. I'd just like to have some idea so I know if I can drive my LED's directly from the digital output or if I'll need to control them with transistors to get the output current I need. So another related question is what is the current limit for the digital outs? I'd assume 5-10mA or so would be the case since the hardware tutorial on LEDs suggests driving LEDs direct from the digital outs.

For a little background on the plan... I've got a couple RGB LEDs going into an omnibot. I'd like to be able to PWM each color independently to control the brightness and color of the eyes. The LEDs I chose are common cathode because I was planning on driving them directly from the digital outputs, but now I'm wondering if I would have been better off with common anode and N-channel or NPN transistors that pull each color to ground on command.

Here's an example photo of how the green looks...

User-inserted image

Skip to comments


Upgrade to ARC Pro

Subscribe to ARC Pro, and your robot will become a canvas for your imagination, limited only by your creativity.


Well, in case anyone out there has any interest in RGB LEDs for Omnibots, I decided to make a second LED board for the eyes. This time I put common anode RGB LEDs in it and used N-channel MOSFETs. That way I can be sure their current won't be limited by the pull up resistors on the EZ-B v4. Sometimes the best way to be sure something won't be an issue is to design around it in the first place.

Also, here is a convenient way to combine the 2 LEDs, resistors and MOSFETs onto one easy to remove PCB. The friction fit of the 2 LEDs into the optics of the Omnibot hold it securely in place when you want it to. User-inserted image

I did find some interesting cheap switching regulators for projects like this as well.

Buck-Boost 5A DC Converter ($5 from China) - you can set them to whatever voltage you want, set by trimpot, and the dropout is virtually nonexistent. What this means is you can follow up that 6V battery in your Omnibot with one of these and get regulated 5V for those intolerant sensors and devices. I haven't figured out how to get the regulator to "boost" and wonder if it truly even has this function, but it works excellent as an accurate wide-range buck regulator with great power output capability in a very small package.

User-inserted image


@bstaehling while I cant answer your question regarding the "pull up resistor in the EZ-B V4 " I am sure someone more knowledgable will chime in!:) . As far as the "boost" word I think that regulator only takes a higher voltage and drops it down ie 12 volts to 6 volts or whatever the trim pot is set at which works great for those servos who are capable of higher then 5 volts. Good pics and keep knitting baby booties until the baby arrives!:D ( I am in "waiting for grandchild mode " ) at the moment


@irobot58 Haha... The good thing about waiting is that it gives you time to think about things and plan them out thoroughly, one booty at a time.

I was hoping I could get the DC converter to work in boost mode as well, but don't really need it for this application. It was a cheap buy with free shipping mail order from China, no instructions, just input, output and a couple unlabeled trimpots. One of the trimpots adjusts output voltage (but maxes out at the input voltage). The other trimpot I'm guessing sets a current limit on the output. It's baffling to me that DC converters capable of both buck and boost functionality are not more prevalent. It seems like buck converters dominate the market with an iron fist, yet I continually come across applications that require extremely low dropout and conditions where the input voltage may vary either higher or lower than the desired output voltage. Where are the low cost flyback and inverter designs at?

At any rate, good to hear from you and congrats on the new expected grandchild.