SmartMaker IMP002 kit

Hi, I’ve got the IMP002 kit and assembled it on the breadboard.
I’ve brought up a number of IMP001s, so got the general idea of what the bring up sequence is.
Powering on the IMP002 it comes up flashing RED as expected.
However when I try the blink up - it doesn’t seem to detect it. I’m using a tablet that has worked with IMP001s (just).
When I look at the bias resistor - a 100K in series with the XRN130W on a scope I’m getting about a 150mV pulse variation while blinkup is running.
The IMP002 module spec says should be looking for 500mV swing.
With a desk light focused over the photo-transistor I seem to get 500mV transitions - but not with a tablet running blinkup.
Any thoughts what might be a better way of coupling light into the phototransistor or making it more sensitive?

My experience:

  1. Make sure the photo-transistor is in the correct way around.
  2. Tie VREF to 3.3V
  3. I’ve successfully blinked up 4 imp002’s with 100K bias resistors, using SMT and TH phototransistors. Keeping ambient light low doesn’t hurt.

I never had to tie vref to 3.3…and I believe my bias value was 220kohm

Yeah, that’s what Dimitri said as well. I would have never tried it if Hugo hadn’t recommended it. I spent a week scratching my head over that one, and now I don’t have any issues.

I believe a range of bias resistor values will work. 100K is the value used in the Amber board.

Thanks for the suggestions.
I did get it blinked up and now trying to figure out why.
I was in a hurry and replaced the bias R with 1M because I had it on hand, and it blinked up.
Now going back reviewing all the connections and photo diode specs to make sure I understand why.

Both the imp002 spec sheet and the new document on building impees state that VDDA is used by the ADC, and therefore by the blink-up circuit. Unless you are using a separate voltage reference, it seems critical that VDDA be tied to 3.3V/VDD.

I’m going to hazard a guess that if blink-up works without VDDA tied to VDD, that perhaps VDDA is floating close enough to 3.3V to get a workable reference, with respect to the bias resistor value? Maybe someone can validate or trash that theory.

Hi jwehr, thanks for the comment, i’ve been focused on a website upgrade.
The IMP002 has been running the last 10days reporting its Vbat.
On the datasheet its says VDDA "ADC reference voltage input. If unused, connect to VDD"
I’ve got the IMP002 Smartmaker Vref connected to an accurate stable low noise 2.048V .
However, I’ve got a general question I’m wondering if anybody can reflect on or point me to the right place - I’m using hardware.voltage(); and its returning 2.056–>2.058 volts when its actually 3.3V The doc reference says that hardware.voltage() uses STM32’s internal voltage reference,
Here is the pic of the voltage,

Yep, this is a documentation error. We can only read Vref on the current modules. If you needed to read supply voltage, you need to use an ADC pin.