I have to confess I have a thing for small prototyping boards, especially ones with Bluetooth or WLAN connectivity. So when I was offered the opportunity to get a couple of Seeed Studio's tiny Bluetooth devboards with Nordic's nRF52840 in them to try out, I jumped at the opportunity. So full disclosure, I did not buy these myself, but neither did I get any compensation, so what follows will be rather unbiased first impressions! I will cover:

1. The basic specifications of the two units
2. How to (re)program the device with Arduino
3. Help to troubleshoot upload.tool.serial errors on Arduino
4. Tips and notes on using the USB mass storage mode
5. Initial summary

I'm interested in trying out the PDM microphone, accelerometer and BLE functionality later on, so check back for updates!

Basic specifications of the Seeed XIAO BLE nrf52840

The Seeed XIAO BLE units come in two varieties, both sharing quite beefy specs:

• Bluetooth 5.0 with an onboard antenna
• Nordic nRF52840, ARM Cortex-M4 32-bit processor with FPU, 64 MHz
• Low power consumption and battery charging chip for untethered IoT use cases
• Onboard 2 MB flash

Additionally, the Sense variant contains a PDM microphone and a 6-axis accelerometer. The units arrived from China quite quickly and came in sweet little Seeed plastic packages, pin headers included (not soldered in):

You can get both directly from Seeed, with very reasonable $9.90 and $15.99 price points. Nordic's chips are quite hard to source from AliExpress cheaply (yes I have looked :), so I'd consider both pretty much a bargain.

Board quality seems very good, pads are shiny and components well placed. The USB port is of modern USB-C variety, and the form factor is really small, just 20 x 17.5 mm or the size of a nickel x dime. and the thickness of a half dollar or so (U.S. readers, you're welcome!). The PCB is one-sided which makes it easy to embed in various configurations.

Outside differences of the basic model and Sense variant is one additional chip that contains the PDM microphone. I think the accelerometer is hidden inside the (seemingly FCC and CE compliant) shielding.

There is also an absurdly tiny reset button on the opposite corner to the microphone pad (top left above) that is a bit tricky to press. I'd prefer a slightly larger one, but it beats shorting pins any day.

Classic blink test with Arduino

You can follow the instructions on Seeed Studio wiki to install the necessary development tools to build firmware for the device. Short version:

1. Get Arduino
2. In File > Preferences, add https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json to Additional Boards Manager URLs
3. Go to Tools > Board > Boards Manager, search for "seeed nrf52" and install the two libraries.
4. Now you can select your board and port.

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Just a small note / Gist type of thing for today: I got tired of adding w.Header().Set("Access-Control-Allow-Origin", "*") to every handler function in my small Golang web app. I'm using Julien Schmidt's excellent httprouter module for simple routing. Turns out the Basic Authentication example is quite simple to adjust for a set-and-forget type of httprouter.Handle middleware:

// https://github.com/julienschmidt/httprouter middleware to set CORS header
func MiddleCORS(next httprouter.Handle) httprouter.Handle {
	return func(w http.ResponseWriter,
    r *http.Request, ps httprouter.Params) {
		w.Header().Set("Access-Control-Allow-Origin", "*")
		next(w, r, ps)
	}
}

Using the middleware is simple, just wrap your normal handler function:

router.GET("/someurl", MiddleCORS(SomeURLFunc))

Or both the middleware and the function it takes implement httprouter.Handle, you can just chain multiple middleware with MiddleCORS(AnotherMiddleware(SomeURLFunc)).

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I got tired of the fact, that Philips Hue application does not seem to have any easy way to set multiple lights to different colors (and possibly brightnesses) at once. Thankfully, there is a great "REST API" to query light and set status! Read on how to query your lights, set them, and do RBG to Philips Hue XY (or X, Y) colorspace conversion with Python!

Connecting and configuring your Philips Hue for API access

This is a prerequisite step. Find out your Hue Brige's IP and create a user (simple method of authentication). It's all covered in Get started.

Write down your IP and the username, and proceed to activate your user and test it according to instructions. Once you are done, you should be able to also open the lights list in your browser and see a lot of info:

https:///api//lights

Listing Your Connected Philips Hue Lights with Python

Alright, with the prerequisites done, let's do a simple test with Python, and query that same address parse the returned JSON, and pretty print it. You'll need Python 3.10+ for this:

import urllib.request
import ssl, json, pprint

context = ssl._create_unverified_context()

def get_json(url):
    """Do a HTTP GET request and return response parsed as JSON."""
    print(url)
    req = urllib.request.Request(url=url, method='GET')
    f = urllib.request.urlopen(req, context=context)
    print(f.status, f.reason)
    return json.loads(f.read())

# Replace these with your config
user = 'yourverylongusernamestring'
ip = '192.168.1.123'

data = get_json(f'https://{ip}/api/{user}/lights')

pp = pprint.PrettyPrinter(indent=4)   
pp.pprint(data)

for k in data: print(k, data[k]['name'])

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I wanted to gift some bitcoin to a friend, and came up with a fun idea of writing them a poem with words making up an BIP-39 mnemonic word list. Then they can easily type in the 12 words in Electrum and take control of their wallet (and maybe transfer the amount to a wallet I don't have access to :).

BIP-39 Fundamentals

Basic idea of BIP 39 is that there is a wordlist of 2048 words, so each word choice encodes 11 bits (2^11 = 2048) of entropy. With 12 words, you have 12*11=132 bits, enough for 128 bits of of true entropy and a 4 bit checksum. You can read all about it in the BIP-39 itself.

Now only problem is, that the last word is not random, but must match the top 4 bits of SHA256 checksum of the preceding 128 bits. So essentially you can choose the 11 first words, and then try to see which choices of 12th word end up with a valid word list mnemonic.

One could manually type stuff into Electrum word list box, but trying 2048 options sounds pretty frustrating (on average, every 16th try will work). So let's do it in Python!

Validating a BIP-39 word list in Python

First, grab the English wordlist — and yes BIP-39 is not the best way as it depends on the word list, but it is standard enough. Then we read it in with Python:

import hashlib, binascii, sys

nums = {}
wordlist = []
with open('english.txt') as fin:
    i = 0
    for word in fin:
        nums[word.strip()] = i
        wordlist.append(word.strip())
        i += 1

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Just a quick note after yesterday's S2 Pico OLED tutorial. I encountered some hiccups getting Serial.println() to work on Arduino with this board. Essentially nothing would come out of Serial Monitor after reprogramming.

I think the core of the issue is that the ESP32-S2 has native USB. ESP8266 and older ESP32 boards used a USB serial converter chip, so programming over serial vs. printing to serial happened without any glitches to the USB. Now with native USB I think here's what happens:

1. You press Button 0, cycle Reset and release B0
2. ESP32-S2 boots into "programming mode" and initializes native USB as COM port
3. You hear the USB connection sound as COM port is assigned
4. Arduino reprograms the flash
5. You manually press reset
6. USB COM port actually drops at this point
7. When you have Serial.begin(); in your code, it now initializes native USB as COM port again
8. You hear the "USB chime" again from your computer, and COM port is assigned

Now if you're used to having Arduino Serial monitor open all the time, the same COM13 that was there during programming on my PC is now a "new" COM13. It seems the serial monitor doesn't notice the change. Solution is simple:

1. Reprogram your chip.
2. Reset, wait for the "chime"
3. Only now open the serial monitor

The irksome thing is, that I'll now need a delay in setup() to see what's going on. Maybe I have an old version of Arduino or something. If you know another solution, you're welcome to drop me a line (me at codeandlife.com)

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Just received the Wemos S2 pico board from AliExpress, and thought I'd write a simple tutorial on how to use it with Arduino, as Wemos' Getting started guide was a bit outdated on Arduino config and did not have an OLED example.

Quick Background

I've been planning to make a DIY hardware Bitcoin wallet just for fun. To make it even remotely secure — once you assume attackers have your internet connected devices pwned it pretty much varying degrees of tinfoil — it's essential that you have an external display and a button to print out your secret key or which address you're signing your coins to go.

My ESP8266 supply was running low (have been using ), and not sure if it has enough memory, I looked what Wemos might have nowadays, since I've used their nice D1 Mini in several projects, such as the ATX power control. I was very happy to discover they had this Wemos S2 Pico available at a reasonable 8 € price point from LoLin AliExpress store , having an SSD-1306 compatible OLED display and even a button. Perfect!

Note: there are clones for Wemos products for cheaper, but I like to show my support even if it costs a dollar or two more!

Setting up Arduino for ESP32-S2 Support

Following Wemos' Getting Started tutorial, I realized the Boards list did not include any ESP32-S2 modules. I checked that I had the "latest" 1.0.6 version installed. After some googling lead me to this Adafruit page, I realised that I needed 2.0.x version that is served from a different location (latest ESP32 branch now lives in Github).

After following the installation instructions — essentially replacing the old Espressif "Additional Boards Manager URL" in Arduino Preferences with the new one — I updated the ESP32 package to 2.0.1 and voilà: There is now the "ESP32S2 Dev Module" available in the ESP32 Boards section. Since Wemos' instructions, the USB CDC setting had changed a bit, this is how I set it up (changes made highlighted):

Note that the S2 Pico requires you to hold Button 0 down, press Reset button and release the Button 0 to enter flashing mode. This will change the COM port! Thankfully, it seems to stay in that mode so you should not be in a rush to flash.

Using The OLED on Wemos S2 Pico

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