Hammerhead Karoo First Thoughts

A few people have asked me my thoughts on the Hammerhead Karoo 2.

Executive Summary

  • it is big – this is good and bad
  • the screen is good, working it in gloves is interesting
  • navigation is excellent – love the climber function
  • battery life seems solid
  • route planning is satisfactory
  • ride tracking link seems reliable (I put in a sim card today, but not sure that is required given hot-spotting worked very well on the first two rides)
  • no need for a phone app to change what is displayed, but it is clunky
  • connection to power crank is intermittent (appears to be a known problem and I will try the fix)
  • phone notifications work but are hard to read

It is big

It is about twice the size of the Bolt. This is good for clarity, not so good for weighing down the mount on my BLENDR mount! I tightened the BLENDR a bit for the second ride to avoid the droop but it still sagged, so I will be a bit braver and tighten it some more.

(I had to buy the £12 plastic puk for the BLENDR mount and use the Karoo Garmin adapter. It would be good if Trek made a Karoo mount puk, but hey ho. N.B. Wish I had seen this before buying from Trek!

The screen is good, working it in gloves is interesting

The screen is very good – really clear in the Sun, especially if you whack the brightness up. I love the colour. I was using thin full finger gloves on both rides. They work on the screen but I think they are getting my fingertip through the material so hitting the right place is a challenge. I switched to mits as it warmed up and then it was fine.

Navigation is excellent – love the climber function

You get the next turn on all the screens so can look at data, knowing it is 1.6km to the next turn. This is a really nice feature. You get all the turns via visual and audio alerts. This is excelelnt. I don’t know if it would do that if I upload a gpx though because I have only used rides I made in the Hammerhead Dashboard.

Climber function is great – it gives a graphic of the climb broken down in to sections by gradient. It also decides how many climbs are on the route and counts them down – “Climb 4 of 8” or whatever.

One weird thing. I made a route starting about 100m down the road from the house if I turned left. When I set off it guided me to the start – turning right and the whole way around the block!

Battery life seems solid

No concerns, I was out for about 5h today and don’t think it got close to 50%.

Route planning is satisfactory

I made my routes on the dashboard by clicking. It doesn’t do popular roads like Strava and put in one or two crazy little detours where you loop off the main road for 100m. Easy to ignore, but weird.

Ride tracking link seems reliable

Wahoo were good that they send a unique link each ride, but bad because the tracking was very hit and miss. I have cycled round the World occasionally. Specialised was good when it worked, but getting it to hook up to the phone via bluetooth was hit and miss.

(I put in a sim card today, but not sure that is required given hot-spotting worked very well on the first two rides)

The first two rides I hotspotted my phone and linked to that from the Karoo. This was very reliable. Today in 5h my phone went from 85% to 35% so 10% an hour. Not too bad.

I had ordered a sim (lyca mobile 1p a month for 6 months for 3GB, cancel any time – I will believe it when I see it) and stuck it in today. I think the Karoo does about 1MB an hour (based on one search) so that is 3000h of cycling a month. Given there are only about 700h in a month, that should be enough! It should even update itself.

No need for a phone app to change what is displayed, but it is clunky

There is an app which purely gives the karoo access to phone notifications. It is a relief not to have to set up everything on the phone like the Wahoo. But changing things as you pedal along involves way too many screens and I have not found an easy way. With no manual in the box you have to work it out, so what I have worked out is the following to change, say, speed to heartrate: swipe down, swipe across, click profiles, click apps, click screens, swipe to screen, click speed, select heartrate, click back, back, back, back, back, back, back, back, select Profile. In gloves that is is a bit of a trial!

Connection to power crank is intermittent (appears to be a known problem and I will try the fix)

You can see the purple line drops out a lot. I have fresh batteries in the crank.

Hammerhead seem aware so I will try their fix and if it doesn’t work, send off the .fit they ask for.

Phone notifications work but are hard to read

So the phone app is very basic but does get notifications to the karoo. But getting them up then reading them is a bit crap. Firstly when you open them they scroll up out of view, secondly when you try and pull them back down they close, thirdly if you finally make it, there are hardly any characters.

yfinance 0.2.3 on raspberry pi

I have a silly little script that checks the shares each day and sends me a telegram, but it stopped working. After an hour or so of analysis I determined that the version of yfinance on raspberry pi that I had, 1.74, was returning None on any call. If I upgrade to 2.3 on Windows (update pip,pip install -upgrade pip, then pip install –upgrade yfinance, it all starts working again.

Getting it to work on Raspberry Pi was not so simple. This is a record of what I did.

Show the currently installed packages in the venv

source ./.venv/bin/activate
pip list

Upgrade pip and try to upgrade yfinance

pip install --upgrade pip
pip install --upgrade yfinance

You get an error saying that rust is the wrong version. Doing sudo apt install rustc does not install a version of rust that is high enough. So you turn to rust istelf and use:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh 

Then follow the instructions. You need to kill the shell or read the message and source “$HOME/.cargo/env”. Then try to upgrade yfinance again.

pip install --upgrade yfinance

It now fails with:

error: command '/usr/bin/arm-linux-gnueabihf-gcc' failed with exit code 1
note: This error originates from a subprocess, and is likely not a problem with pip.
ERROR: Failed building wheel for cryptography
Failed to build cryptography
ERROR: Could not build wheels for cryptography, which is required to install pyproject.toml-based projects

So try to get gcc working. I read that installing gcc libffi-dev libssl-dev and python3-dev might help so did that, though I already had gcc and python3-dev installed so just needed this:

sudo apt-get install libffi-dev libssl-dev
pip install --upgrade yfinance

And THAT fixed it 😁so I now have yfinance 0.2.3 and yfinance works.

arduino as mqtt temperature sensor

My office gets pretty cold and I had worried that the heater would come on if it went below 5°C. This was until I went in there and discovered that the thermostat from Honeywell will not read lower than 5°C!

Now I have grafana I was wondering how to get a reading of the temperature in there. I have lot of kit kicking around from my arduino days so I thought I would give it a whirl. The aim was for the arduino to push the current temperature to the mosquitto broker on openhabian then read it out to influxdb and eventually to grafana.

I ended up using:

  • arduino uno
  • arduino uno ethernet shield
  • DS18B20 temperature sensor
  • 4.7 kΩ resistor
  • breadboard and leads


I used this to remind me how to get the temperature sensor working: https://create.arduino.cc/projecthub/TheGadgetBoy/ds18b20-digital-temperature-sensor-and-arduino-9cc806. Then with a bit of searching and playing around I got the whole kaboodle working. There was a lot of intelligent copy and paste and I have no idea how much of this is redundant but it bloody works (code below).

Weirdly, the graph sparklines did not work in the temperature display in grafana. https://community.grafana.com/t/sparkline-does-not-appear-on-single-stat-graph/566 helped me work out that I needed to do a GROUPBY in the query (I used 15m). You can see the result at the top of the page.

// First we include the libraries
// Temp Sensor
#include <OneWire.h> 
#include <DallasTemperature.h>
// Ethernet Shield
#include <SPI.h>
#include <Ethernet.h>
// Mqtt
#include <ArduinoMqttClient.h>
// Data wire is plugged into pin 2 on the Arduino 
#define ONE_WIRE_BUS 2 
// Setup a oneWire instance to communicate with any OneWire devices  
// (not just Maxim/Dallas temperature ICs) 
OneWire oneWire(ONE_WIRE_BUS); 
// Pass our oneWire reference to Dallas Temperature. 
DallasTemperature sensors(&oneWire);

// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

// Set the static IP address to use if the DHCP fails to assign
IPAddress ip(192, 168, 0, 23);
IPAddress myDns(192, 168, 0, 1);

EthernetClient net;

MqttClient mqttClient(net);

const char broker[] = "openhabian";
int        port     = 1883;
const char topic[]  = "arduino/temperature/";

char clientId[] = "ToM_arduino_001";
char username[] = "openhabian";
char password[] = "averybigsecret";

const long interval = 1000;
unsigned long previousMillis = 0;

void setup(void) 
 // start serial port 
 Serial.println("Dallas Temperature IC Control Library Demo"); 
 // Start up the library 
  // start the Ethernet connection:
  Serial.println("Initialize Ethernet with DHCP:");
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    // Check for Ethernet hardware present
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
      Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
      while (true) {
        delay(1); // do nothing, no point running without Ethernet hardware
    if (Ethernet.linkStatus() == LinkOFF) {
      Serial.println("Ethernet cable is not connected.");
    // try to configure using IP address instead of DHCP:
    Ethernet.begin(mac, ip, myDns);
  } else {
    Serial.print("  DHCP assigned IP ");
  // give the Ethernet shield a second to initialize:

  Serial.println("You're connected to the network");

  // You can provide a unique client ID, if not set the library uses Arduino-millis()
  // Each client must have a unique client ID

  // You can provide a username and password for authentication
  mqttClient.setUsernamePassword(username, password);

  Serial.print("Attempting to connect to the MQTT broker: ");

  if (!mqttClient.connect(broker, port)) {
    Serial.print("MQTT connection failed! Error code = ");

    while (1);

  Serial.println("You're connected to the MQTT broker!");
void loop(void) 
 // call sensors.requestTemperatures() to issue a global temperature 
 // request to all devices on the bus 
 Serial.print(" Requesting temperatures..."); 
 sensors.requestTemperatures(); // Send the command to get temperature readings 
 Serial.print("Temperature is: "); 
 Serial.print(sensors.getTempCByIndex(0)); // Why "byIndex"?  
   // You can have more than one DS18B20 on the same bus.  
   // 0 refers to the first IC on the wire 
   // call poll() regularly to allow the library to send MQTT keep alives which
  // avoids being disconnected by the broker

  // to avoid having delays in loop, we'll use the strategy from BlinkWithoutDelay
  // see: File -> Examples -> 02.Digital -> BlinkWithoutDelay for more info
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) {
    // save the last time a message was sent
    previousMillis = currentMillis;

    Serial.print("Sending message to topic: ");

    // send message, the Print interface can be used to set the message contents



influxdb and grafana


I have long wanted historical data on temperatures. Not sure why, but it might be interesting. Enter the influxdb persistence plugin and grafana (now I need to work out how to back them up too I guess).

Backing up influxdb turns out to be easy and I will add this to the backup script:

influxd backup -portable -database openhabian /mnt/nas/backup/openhabian/influxdb

rpi can just about run inlfuxdb 1.6 and can be installed by apt, and was enough. I just followed the instructions below then set it up in OpenHAB. I then had to work out how to actually store information in teh database. grafana was much easier.

Influxdb notes

  • https://docs.influxdata.com/influxdb/v1.6/introduction/installation/ but I used apt then followed the configuration instructions
  • You need to go in to the CLI and create a database, user and password which are then configured in openhab.
  • Then edit /etc/openhab/persistence/influxdb.persist – not sure about the line “Temperature* : strategy = everyHalfHour, everyChange”
sudo vi /etc/openhab/persistence/influxdb.persist 


Strategies {
    everyMinute : "0 * * * * ?"
    everyHour   : "0 0 * * * ?"
    everyHalfHour       : "0 0,30 * * * ?"
    everyDay    : "0 0 0 * * ?"

    default = everyChange

Items {
    Tasmota4Fridge_Tas04PowerNow  : strategy = everyMinute
    Tasmota2_Watts  : strategy = everyMinute
    EMONPIMQTTThing_HousePowerwatts : strategy = everyMinute
    KitchenEvohome_Temperature : strategy = everyHalfHour, everyChange
    MasterBedEvohome_Temperature : strategy = everyHalfHour, everyChange
    Tasmota01PowerNowW : strategy = everyMinute, everyChange
    Tasmota3TVStack_Tasmota03PowerNow : strategy = everyMinute
    WeatherandForecast_OutdoorTemperature : strategy = everyHalfHour, everyChange
    emonpiMQTTThing_EmonPiExternelTemp : strategy = everyHalfHour, everyChange
    SnugThermostat_Temperature : strategy = everyHalfHour, everyChange
    Temperature* : strategy = everyHalfHour, everyChange


grafana notes

I just did all this then set up influxdb and created some graphs:


There is no obvious backup solution yet, but I will explore this: https://github.com/ysde/grafana-backup-tool

Backing up Openhabian

I am using OpenHab more and more and not having a backup was starting to worry me. There are better solutions, but this works for me. I have a 1TB usb PCIe HDD which the OpenHabian is now running as the house nas, and this solution makes a backup each night and copies the newest file to the NAS with a full backup each Sunday.

It has to be run as root cron:

sudo crontab -e -u root

Then this is the cron for root:

10 2 * * * /home/openhabian/bin/backup-openhabian.sh

And this is the script:


#  MUST be run by root cron!!
if [[ $(date +%u) -gt 6 ]]; then
    openhab-cli backup --full
    openhab-cli backup

# Copy to the nas
echo Copying the newset file to the NAS folder...
file=$( ls -t /var/lib/openhab/backups/* | head -1 )
cp $file /mnt/nas/backup/openhabian/

# delete files older than 7 days
echo Deleting anything older than 7 days...
find /var/lib/openhab/backups/* -mtime +7 -exec rm {} \;
echo Done!


https://community.openhab.org/t/solved-backup/57666 is for OH2, but I guess it will work the same. I really need to practise that with a blank SD card.

sudo systemclt stop openhab
openhab-cli restore /var/lib/openhab/backups
sudo systemclt start openhab