External BlinkUp LED behavior

For my most recent project, I want to use external BlinkUp circuitry on a P3V3 (from TheMakeDeck). Their video does a great job of explaining what to do–it’s pretty simple.

However, I’m seeing amber when it should be dark. I’m using the SunLED XLMDKVG34M bi-color lamp. I’m seeing 1.9v on the red and green leads when it should be dark. I’ve swapped the red and green leads several times and have power cycled. I see the device in my IDE, so I know it successfully blinked up. Thoughts?

Not sure if you are getting all of my emails. Just to verify… You are using this LED, http://www.sunledusa.com/products/spec/XLMDKVG34M.pdf, which is common cathode, correct?


Sounds like you do not have the 10k across the red LED? This has resulted in the imp misdetecting the type of the LED (common cathode/common anode) and hence thinks it’s turned it off when in fact it’s turned red and green on.

That’s something that @MakeDeck had suggested, but I checked and all seems OK in that regard. I also removed the external components and re-soldered the two solder jumpers on the P3V3 and the onboard lamp worked just fine. To me, that points to the SunLED bi-color lamp behaving differently than the LiteOn device shown in the @MakeDeck video. I need to order a few of those and see how they perform.

After a little more thought on this… the SunLED’s are actually working, they are just being driven backwards, so the problem does have to be somewhere else.

On the P3V3 that I was originally using where I re-soldered the jumpers, I see 3.3 volts on RD and GR and everything works as expected. However, on the P3V3 that I’ve connected the external lamp (after “removing” the solder jumpers), I see 1.9 volts on RD and GR. This would seem to indicate it thinks it’s a common anode instead of cathode? What’s odd is that both devices work normally when restored to original condition. Are the LEDs on the P3V3 in a common cathode or common anode configuration?

The SMT component on P3V3 is common anode. RD and GR are connected to the cathode side of that device, so when they are connected by the solder jumpers, you are measuring the voltage on the cathode side.

I tested a Revision 2 P3V3 this morning with a LITEON part successfully.

What voltages do you see on either side of R4? You should see close to 3.3V on the bottom side, away from the imp, and close to zero volts on the top side.

I’ll check on what you’re asking, but…I just added an external 10K resistor from RD to ground and it’s working fine.

(updated) recall…this is the version without the P3V3 and MakeDeck labels.

Without the schematic, I’m a bit confused as to how the 10K from the RD to 3.3V on the common anode gets switched to 10K to ground on the common cathode.

It doesn’t. You have something else going on if a pulldown resistor on RD makes it work. R4 is a pullup to 3.3V with either common anode or common cathode parts installed. The imp uses it to determine which is there.

Where you able to check R4 without the additional pulldown?

Voltage is 3.3 on side closest to imp and 1.9 on the other side. This is on a P3V3 without “MakeDeck” on the top.

I had been swapping the RD and GR leads to get it to look somewhat “normal”, but they are now in the proper configuration–the same as with the external 10K. It’s on solid amber when it has finished BlinkUp (during BlinkUp is alternates between red and amber).

So, I’m confused as the data sheet shows using a 10K to ground on common cathode configurations.

Hugo, Can you weigh in on this, please. Your comment above indicates the 10K resistor should be “across the red LED”. If I have a common cathode, going from RD to ground would be across, but not if it’s RD to 3.3V. All of this is said without first hand knowledge of the circuit on the P3V3.

As I said, the 10k should be across the red LED.

This means it’s to ground on common cathode and to 3v3 on common anode.

Where’s the 10k on the P3V3? Is it possible that’s still connected when you disconnect the on-board LED? There’s no issue with the SunLED part, we use that one on Lala as I remember.

@MakeDeck in a PM said I should remove it after it was realized the recommended circuit had changed after the P3V3 design. With the onboard 10K in place, the external 10K simply creates a voltage divider that presents a low enough voltage that the imp002 considers it a common cathode and it works fine. With this confirmed, @MakeDeck will simply need to recommend adding a 10K across the external LED if it’s a common cathode device and not worry about the onboard 10K.