The blog of 'The Arduino Guy' aka Mike McRoberts, author of Beginning Arduino.

21 October 2013

DIY Sous Vide Cooker Project

I had seen plenty of websites or videos of people making their own sous vide cookers so thought I would give it a go myself. If you don't already know, sous vide is a method of cooking food in sealed bags in a water bath with the water held at a very precise temperature. The food is cooked for a long time and means the food is cooked perfectly evenly throughout instead of cooked well on the edges and not so well in the centre. A perfect steak for example would be the exact shade of pink you wish from edge to centre. As a huge steak fan and having had some fantastic steaks in expensive restaurants but been unable to reproduce them at home I wanted to try this out.

I already had a slow cooker and at first intended to hack it for temperature control. But after using an Arduino and a DS18B20 temperature sensor I was able to determine it was capable of reaching the target sous vide temperatures easily and beyond. So I decide to make an external temperature controller box instead. I was originally going to use an Arduino and a relay, but found out you can buy temperature controllers cheaply on eBay for a lot less than the cost of an Arduino and a relay. So I bought a cheap PID temperature controller for about £10, a project box and a few other parts and set about making the unit. 

These units are fully controllable with either a high or low temperature setting, temperature alarms, time delays and so on. They are very easy to wire up (despite the crappy instructions you always get with Chinese made electronics).

The steak I cooked on the very first time I used the unit was cooked perfectly throughout and was, without exaggeration or bias, the most tender and delicious steak I have ever had outside of a top London restaurant. Even my partner, who was very sceptical about the whole thing, admitted that the steak was the most delicious she had ever had and was very impressed. For a total cost of around £35 I have made my own sous vide cooker and cooked an amazing steak without shelling out the £100's it would normally cost to buy a domestic sous vide cooker. I will definitely be cooking all of my steaks the sous vide way from now on. 

A lot of people use rice cookers instead of slow cookers as the thin walls mean you are able to control the temperature more precisely. If I didn't already have a slow cooker I would have purchased a rice cooker. However, the slow cooker works extremely well also. 

As I made an external controller instead of hacking the slow cooker this means the cooker is still fit for purpose and is still safe. Also, I can plug anything I want into the unit and give it temperature control, such as a heater, fridge, freezer, home brew kit, aquarium, etc. 

I've made a video (see below) that shows the full build and if you want further information then contact me on Twitter, G+ or Facebook using one of the methods listed at the end of the video.

04 October 2013

Telescope Focus Controller - Part 1 - The Idea.

One of my hobbies is astronomy and more specifically, astro-photogaphy. I have a pretty sophisticated setup with a computerised GoTo mount with a cooled CCD camera, motorised filter wheel, guide camera, etc. Most of the gear is automated and can be controlled remotely (i.e. it is out in the cold while I sit in the 'control room' indoors and operate it. however, the one thing that still has to be operated manually is the focuser. I have no choice but to focus the kit out in the cold then come indoors. Not only will automating the entire kit make it more comfortable to image when i'm at home, but it will also save a lot of time and time is precious when doing astro-photography, especially in windy and rainy old England.

Me & my astro gear - Brecon Beacons Astrocamp, Sept 2013
Now a commercial motorised focuser isn't cheap. They can cost a lot of money and most of the cost is unnecessary. After all, it is simply a stepper motor attached somehow to the focus knob and then controlled with a 'box of tricks' connected to a PC. So in the hacker spirit I decide to make my own. I had an old 3.15v Sanyo stepper motor somewhere that I scavenged from a printer or scanner or something so decide to use that. I also had an Easy Driver 3.1 board (i've also got Adafruit motor shields and the official Arduino Motor Shield).

As the completed product needs to be small and light I went for the Easy Driver motor control board as it is tiny and easy to use. 

So far I have hooked it up to the motor and have it stepping in tiny 1/8th microsteps. The next stage is to create a control box with knobs and buttons to select the motor speed and to focus in and out (Stage 1). This will also have a USB interface so I can connect it to a PC and control it from software (Stage 2). This will have a temperature sensor so it can automatically compensate for the changing temperature throughout the night as the telescope cools down and heats up. 

Once I can control it from a PC I can then operate it remotely over VPN and sit in the warm whilst imaging. 

Stage 3 of the project will be to write some ASCOM complaint drivers for the device so I can hook it up to either FocusMax or my imaging software (APT & MaximDL) so the focussing procedure can then be fully automated.

As you can see in the picture I am providing the motor with 6.2 volts. The motor is a 3.15v motor. However, that's 3.15v per coil and so double that is needed to get it going. Powering it with just 3.15v volts and it goes nowhere. When running continuously it was using about 500ma. 

Next I am going to make a hand control unit. The plan is there will be a knob to select the step speed and number of steps. Then buttons for focus in/out, another for selecting continuous operation or one iteration of number_of_steps and another for selecting either speed or steps. This will be displayed on either a 7-segment display or an LCD. 

Below is an example video showing the motor in micro-stepping mode. it is doing 1/8th micro-steps controlled by an EasyDriver 3.1 motor control board. The motor is a 3.15v Sanyo stepper motor salvaged from a printer or scanner. I am running it at 6.2v (3.1v per coil) and have dialled down the ED3.1 so it is being given no more than 100-150mA. Any less and it stalls and any more and it gets too hot. This current is enough to give me the torque I need. Next I am prototyping the circuit and testing it out. I will post an update soon.

Sous Vide Cooker Experiment

So, if you haven't already heard of Sous Vide cooking I'd highly recommend reading a bit about it. In a nutshell, it is cooking food in a water bath at a certain temperature with the idea being that the food cooks slowly and evenly resulting in a perfect steak, or whatever it is you are cooking.

sous vide cookerWith a steak for example, you will usually have a temperature gradient across the meat resulting in a pink centre and increasingly darker and cooked meat towards the edge. With sous vide cooking, the steak is cooked exactly to your specifications throughout the meat evenly. You then finish off the crust of the steak quickly with a blowtorch or in a pan.

However, sous vide cookers for domestic use are very expensive indeed. But, with a bit of time and not a great deal of effort you can make your own for a fraction of the price. Many people hack slow cookers, crock pots or rice cookers into DIY Sous Vide cookers. I happen to own a slow cooker that rarely gets used so I thought I would see if I could repurpose it into a Sous Vide cooker to make the perfect steaks.

So the first thing to do was to find out if the slow cooker could reach the temperatures necessary for cooking sous vide style. Typically you want temperatures ranging between 50-60°C for the perfect steak and up to 80° for other items. So I had a DS18B20 temperature probe lying around so I hooked it up to an Arduino and set it to take a temperature reading every 5 minutes and print that to the serial monitor. That way I could see over time how long it took to get to temperature and if it could reach at least the temperatures necessary for a perfect steak.

Over the next 2 hours the cold water I put into the pot was heated slowly up to around 65°C so I knew it would be ideal for how I like my steak (rare). I decided to leave it on overnight and see just how hot it got. The next morning the temperature was just over 97°C, which was a surprise.

So, I now know that the cooker can be used to cook meat sous vide. All I need to do next is to create a control unit that keeps the water bath at the exact temperature necessary. I will work on that at some point in the not too distant future and will give you all an update.