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#RJamboree 2014 Smithy AKS

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Xmas_bot

Hi,
Please watch the following video & then continue down for a full explanation of what I’ve done to achieve this.

This is a quick update on where I am with my #shrimpbot improvements.

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Above – you can see the 2nd bot I have made. This one has been made with a 3mm orange plastic sheet that the DT dept had lying around. My first bot was made using wood and felt a lot nicer & fitted together a lot more easily. I’m using the plastic as its Xmas & I dont have access to the laser cutter to cut more wooden chassis so Im using these plastic chassis that I had lying around.

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I’m really pleased with the fact that I got the sequence working using what I call the preevolved shrimp setup. It requires just 3 components & the ATMEGA chip & even if I cant get the kids  competent enough to wire this version (unlikely I think) I should be able to put 5-6 of these together myself while the kids are completing another activity.

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Below you can see the previous version which used the Arduino board & a 9v box battery with the phone charger type power connector. It also requires a separate mini breadboard for the circuit.

I’m much happier with the chip & circuit to be contained on the same breadboard. I’m also pleased at my decision to switch to 4 AA batteries & a nice cheap power case. It has clear +ive & -ive leads & Ive positioned it between the two wheels on the bottom layer of the chassis.
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Below – you can see the full board. I bought some flat breadboard cables (brown & purple on the left & green & red on the right) They help keep the profile of the board down and make it much easier to avoid accidentally pulling out cables. Ive included resisters – which I dont think are 100% necessary but I fried an LED 2 days ago by not putting a resister in with it and that’s worried me enough to get me back into the habit! 🙂

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I realised that I could avoid soldering, given the amount of movement the bot performs, as the cabling lodges firmly enough into the small ring terminals of the motors.Image

In the above picture you can see the battery pack & how the +ive and -ive terminals are connected to the breadboards long side rails. using the RED & BLACK cabling.
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You can see in this photo how the YELLOW & WHITE cables attach to the motors.

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Above, you can see the preevolved shrimp setup. It has the additional RED powerIN cable & GREEN GROUND cable which allow the current to jump from the breadboards side rails to the lines that the chip needs it on.
ImageFinally you can see a full view of the Transistors. The signals coming from pins 13 & 11 (LEFT to RIGHT down the BROWN & PURPLE cables are switching the power on & off to the motors through the Transistors. The current is travelling UP the photo, starting on the bottom rail and travelling along the short RED cables before meeting the resisters which help the current jump the gap in the middle of the board. The current then travels up the rails to the LEFTmost side of the Transistor. It cannot pass unless it is receiving a signal from the chip (coming along the BROWN & PURPLE) cables. The current then travels back down the board until it meets YELLOW cables which are power going IN to the motors. The current then returns to the board via the WHITE cables and back along the board (to the LEFT) to the negative terminal on the battery pack.

Development of the #ShrimpBot

Development of the #ShrimpBot

At this point I have built the base of the #ShrimpBot.

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Both motors have been checked by connecting them directly to battery terminals.

I have soldered the jumper cables onto the motors & wrapped them in tape to keep them secure.

I now want to begin the breadboard circuit that will allow me to send a signal to the motors to turn them on & off, in effect steering the Bot.

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In order to test the circuit I’m going to use a spare motor & just push the jumper cables through the wholes in the terminals.

I’ve also blue tacked a toothpick to the axle so its clearer in the video to see whether its turning.

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I’m going to be using a modified version of the 3rd circuit from the Arduino Experiments kit to control the motors.
I can’t recommend the ARDX kit highly enough – its a bit expensive but an absolute MUST if you’re new to this stuff!

http://oomlout.co.uk/starter-kit-for-arduino-ardx-p-183.html

To begin you’ll need to take a Transistor (the black three legged fella) & a Resistor (the ceramic type thing with stripes on it).

The exact position of them along the board isn’t important (ie it doesnt matter if you use row 49,50 or 51) but they should create a T shape.

Also it’s important to check the Transistor is facing the right way – the flat side should be facing towards the Resistor.

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The WHITE jumper cable is plugged in next to the Resistor & I’ve just blue tacked that down to make the photo clearer.

This WHITE cable will be the signal cable – it will be the wire that we send our signal down to tell the motor when we want it to turn.

I have also included a powerpack – I bought this one super cheap from radio Shack but you can get them at Maplin & online.

(I feel duty bound to give a word of caution here as I have had 2, that’s TWO ASDA batteries literally explode on me in the last 2 months –

I will include photos of the remains of them in a separate article – I’m told batteries should never explode but one went in the middle of a

lesson & I have 2 dozen year 8 pupils with frazzled nerves who will attest to how loudly the thing BANGed when it went!!!)

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Although the two stages above look like a big jump in complexity all that I’ve really done is add the motor.

I’ve blue tacked the motor onto the corner of the breadboard. I’ve chosen to use RED as the positive/powerIN lead.

The wires allowing current out of the battery are BLACK & it connects right next to the WHITE signal pin.

The following diagrams make this clearer…

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The circuit is essentially putting a tap on the outflow of the electricity.

The Transistor waits for a signal on the WHITE cable & if it receives one it allows current to flow from the BLACK wire

through the Transistor and on down the BLUE wire back to the negative terminal on the battery pack as can be seen here.

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Now we need to work on putting a signal down the WHITE signal cable to tell the motor WHEN we want it to turn.

At this point I would have MUCH preferred to use the #Shrimp (other wordpress blogs deal with my use of the #shrimp)

However I took advice from Tim Moore of Accrington Academy & am using an Arduino in order to remove as many doubts from the circuit as possible.

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The Arduino already has the Blink sketch uploaded onto it.

You can see this if you compare the two photos – on the left there is only the GREEN power led.

On the right photo (above the MEGA chip on the left) you can see the YELLOW pin 13 led is lit.

This means that pin13 is turning ON then OFF constantly.

We want to attach the white signal wire to pin13 so that the motor is prompted to turn ON then OFF.

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Notice:- The white signal cable is being stretched down to plug into pin13.

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 IMPORTANT: The circuit above uses the Arduino’s 5V or 3V power pin as a substitute for the battery power pack. At present the battery power pack circuit doesn’t work. However I can create a working circuit using both the Arduino’s 5V AND 3V power pin but it’s too complex to show the theory of the circuit & I think it’s important for the pupils to see the understandable circuit implemented before giving them a more complex circuit.

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