Minecraft Server

One of our members Pixelpox has built a Minecraft server for us to all play and socialise on. It is a project that is just getting started but has already been popular with some of the members here at the Sheffield Hackspace.

Interesting Specs

Some of you are most interested in the technical details about the server so here it is.

Server TypeSpigot
Minecraft Server Version1.14
Plugins Addedgriefprotection

Members Creations

Our members have been hard at work collecting resources and building their buildings. Some people have taken to creating farms such as sugar cane and eggs for the whole community to benefit from a sustainable source of food.

Others have been focused on village security and plain old exploring the world. Check out some of the things that have already been built.

How can I join?

It’s simple and FREE! Go to the Sheffield Hackspace Forum to subscribe online and introduce yourself. After that ask for the Minecraft details and one of our current members will get back to you with the details. Our Minecraft servers are also open to friends/family of hackspace members.

Alternatively you can join us on a gaming night that runs every other Saturday, see our events calendar for more details but importantly you’ll need to sign up as a paying member (£6/month) first which can be done on your first visit.

Gaming night isn’t just about Minecraft, members decide on the night what they are going to play in the group, this can be RetroPie and Raspberry Pi games, console games, PC LAN games, board games and much more!.

A Model Lighthouse

Designed and built at the Sheffield Hackspace using an arduino and bits and pieces of things that you might find lying around in your own home…

Here’s the setup:

An arduino (pro mini) for controlling the SG-90 servo motor
An ESP8266 for wifi access and neopixel control
A piece of gutter and downpipe for the main body
A plastic dome sourced from a solar powered garden lamp
An Aldi’s peanut butter jam jar lid (crucial)
Other bits and bobs scrounged from various unwanted poundland items

If you think this is cool wait until you see the boats!

Electromagnetic Field 2016

A great weekend was had by all as multiple members of SHH&M went down to Loseley Park for EMF2016. Our entrepid woodworker, AJ, went ahead of the rest of us to build the sink frames, back of the bar and multiple other items ahead of over 1400 people decending for a weekend of camping. However, as should be expected from a group of hackers and makers camping, electricity and high speed internet were essential amenities. We had our own Village, complete with flag, and took along some Go-Boxes and Bugs’s pancake engraver to show off (blog to follow!).

Events over the weekend included numerous talks from lockpicking to film special effects and latest updates from CERN to magic tricks and illusions. There was also the opportunity to make a wide range of things such as a titanium spork, a patchwork pin cushion and a pin hole camera. Evening events included film showings, the infamous Robot Arms with NottyHacks Barbot, a light maze and FirePong – yep, ping pong with fire! There was also a giant blow up rabbit which you could change the colour of by tweeting a colour!

All the talks are available to watch on You Tube if you feel want to catch-up with anything.

A one day event is planned for next year, with the next EMF camp due in 2018. If this year is anything to go by, both should be highly recommended!

 

Blue Bunny

Blue Bunny

White Bunny

White Bunny

OLYMPUS DIGITAL CAMERA

Red Lightfield

Blue Lightfield

Blue Lightfield

Hacking De-bounce and Rotary Encoders

Prototype console interface for embedded projects

Prototype console interface for embedded projects

At the UK Makerfair during a brief lul the conversation turned to rotary encoders, simply as I had ordered a paw full from china for one of my many projects that simmer along in the background. The picture here shows the initial prototype that I used for this article. The feedback about rotary encoders that I received was that they were terrible and to be avoided. Principally as the switch contacts were very noisy and produced way too much bounce. I was still interested in using them firstly as having done embedded stuff for years bounce is something I consider trivial and fixable, secondly as they make a really cool, easy and feature full user interface using the minimum of pins.

De-bounce circuits

De-bounce circuits

The circuits I most commonly use for de-bouncing simple switch contacts are shown in the picture here. I ran this up in Kicad for the article. Something worthy of note is that Arduino’s and a number of other micro controllers have internal pull-ups that you could use. Do not use these when de-bouncing your inputs. They vary very widely in effective resistance value and the results will be massively variable when used with the same external components. Indeed a quick search of the internet shows a range of circuits and values mostly with a string of comments along the lines of someone found a different value or combination to work better. What is happening here, and why so much variability of what should be a trivial, bread and butter type, of interface circuit.

No de-bounce

No de-bounce

Time to dig out the Bitscope I bought from Pimoroni a while back and capture some waveforms. It will work as a capable enough DSO for this investigation. On the left is the A output of the rotary encoder from the previous picture set-up as a switch with pull-up as per the schematic above. The value of the pull-up resistor in this case is 10K Ohms a fairly typical pull-up value. The large nice square pulses are the outputs from the encoder and the very narrow horrible pulses are the switch noise and bounce. This looks reasonably what I would have expected although the switch looks to be more noisy than bouncy. I spun the input shaft quickly by hand to get enough pulses into shot and it is noticeable that the rubbish pulses produced are proportional to the speed of spin. The other thing that is noticeable is the duration of the pulse are quite short. With a standard press button you can not move your finger that quick and a de-bounce period in software of around 10mS is not uncommon. In this case though, if you did this it is clear that you would be missing a lot of steps from the encoder. Each one of those noise pulses is a full logic value in height and will trigger an interrupt, giving you a wildly incorrect count and wasting a whole shed full of precious processing cycles. I can see why you might think they were to be avoided if you had not de-bounced them in any way.

100nF De-bounce Capacitor

100nF De-bounce Capacitor

Adding a 100nF capacitor as per the above schematics produces the results below. This produces a very large reduction in the height of the noise pulses but they are still large enough to trigger some interrupts, the amount of processor time we waste though is reduced. The number of incorrect counts is also reduced but there are still some present. Also look at what is happening to the corner of the rising edge of the pulses that we want to work with. They are no longer square and are being rounded off. So a big improvement but still not as good as we would like. In a simple switch this rounding etc is not a problem. We are working with a rotary encoder though and the relative position of the edges in each channel is important to us. Where an edge curves too much it becomes unclear where the micro controllers input will decide it has switched from logic 0 to logic 1. If we got such a big improvement for adding in 100nF, will adding in some more be helpful?

200nF De-bounce capacitor

200nF De-bounce capacitor

So lets add in another 100nF capacitor in parallel across the one we put in last time. Taking the total up to 200nF. Yes the noise is reduced much further and we could probably work with that at a push. But look at the state of the rising edges. As we increase the capacitance we increase the loss of definition of the rising edge and consequently our ability to correctly resolve the direction of the encoder. The faster the encoder is turned the more problematic this becomes as the curve remains the same width but the width of the pulse we are relying on has become narrower. We could have kept the capacitance value the same but increased the resistance to say 20K and we would get exactly the same result. The RC network that is cleaning up our signal has a time constant that is proportional to the ratio of the resistance and capacitance that makes up the circuit. It is this time constant that is low pass filtering the pulses and giving us the effects we can see on the scope. Bearing this in mind if we check out the Atmel AVR data sheet, as this is the most popular micro-controller in the Arduino series, we see that the internal pull-ups have a value of between 20K and 50K. So a massive variation in the pull-up value and consequently a massive variation in the de-bounce action and on our pulse edges is produced by this, hence why de-bounce circuits that use the internal pull ups are to be avoided. We need results that are consistent.

For a simple press button a simple RC network as shown in the above works great as it is a very slow logic signal, but what can we do to recover nice square edges on our fast, encoder signal pulses, and get rid of the noise pulses. The answer is to use a Schmitt Trigger which increases the level at which a rising edge will be consider to have switched from low to high and reduces the level at which a falling edge will have switched from high to low. This circuit will ignore the noise pulses that we have reduced in height leaving us with a clean pulse train and nice square edges from our encoder. Check out the linked wikipedia article, ignore the over complicated mathy explanations and control theory waffle look closely at the wave form diagrams at the top right of their page. What is more this circuit is so useful that it comes already built in to a number of inexpensive logic gates. You don’t need to make one.

Unfortunately I don’t currently have the parts to hand to show the fully processed pulse train but the procedure is to add in a Schmitt Trigger logic gate (ie a 74LVT14 or similar)  as per the diagram above, pick the pull up resistor value for your chosen application 10K is good for most applications, looking at our scope waveforms you may want to go to somewhere conveniently around 20K. Then starting with a small capacitance for the de-bounce capacitor increase it until all your noise pulses on the output of the schmitt gate have gone. Using your scope to see when this happens. Once you have achieved this you know what the correct values are and can pick the nearest off the shelf value to use every time and get repeatable results. What’s more you will not be wasting any precious processor cycles on clever de-bounce code and unnecessary interrupts.

Take away points from this are:-

  • Do not use the internal pull-ups with de-bounce circuits it is a false economy.
  • Simple RC circuits are plenty good enough for simple push buttons and switches.
  • You need a logic gate with a schmitt trigger input to clean up the faster logic pulse trains from rotary encoders.
  • You can do a lot of electronics and get an intuitive grasp of what is happening by laying on a scope and laying off the math.
  • Clean up your signals before trying to code them clean, crap in equals crap out.
  • Rotary encoders are great if you know how to work with them.

Mini PIR Sensor

Mini PIR Sensor

Mini PIR Sensor

I bought some of these mini PIR sensors on aliexpress, for the occupancy detector part of my ongoing NoTLamp project. They can be found for just under 1 UKP each. I want the NotLamp to work efficiently as it will be powered all the time. I also want it to all work from a single simple power supply and have chosen 3v3 as the lowest common denominator. I am taking the decision to work at 3v3 more often than 5V these days as so much is produced with 3v3 in mind. A big annoyance is the amount of 3v3 boards etc that are made 5V compliant and then used with other micro-controllers (ESP8266) or Pi’s that are 3v3. Very wasteful of both parts, and electrons. This picture shows the mini PIR sensor on top of a business card and next to a 20p piece so you can get a feel for how mini it really is. These little units are very simple with nothing to adjust and no daylight sensing, they are aimed at whole raft of people sensing switches etc and are designed to work across a wide voltage range from 4.5V up to around 20V. They have the part number DYP-ME003SE-V1 but can also be found online as an HC-SR505. These look to be almost identical bar the addition of a single capacitor on the front. I could not find any schematic for them which was disappointing, all the links claiming to point to a schematic take you to a schematic for the HC-SR501 the bigger brother to this one which uses a larger BIS0001 PIR chip.

Mini PIR Detail

Mini PIR Detail

These pictures show both sides of the board close up and side by side. In the left one you can see a 3v3 linear regulator and polarity protection diode, Those and the PIR detector at the top of the board look to be the only parts that are common between the two types of PIR sensor mentioned above. The IC is half the size of the BIS0001. The output is a 3v3 logic signal. Looking at the left hand image there is an unpopulated footprint to mount an S8050 NPN transistor for switching a relay or level translating the signal. You will also need to remove R1, just next to it if you want to do this. The presence of the 7133 3v3 regulator though is promising for my application as it shows that the circuit itself actually does run at 3v3. Just for the hell of it I tried the PIR at 3v3 and 5v to see how it did. It preferred 5V and worked reliably but dropping the voltage to 3v3 (Actually the test Arduino was putting out 3.73V) gave some interesting results. The device powered up and seemed to work OK but after triggering the detector the first time it re-triggered itself cycling on and off for its pre-set delay period. I counted the delay and it was around 10 seconds give or take a bit. Probing the underside of the board I found that for 3.73V in the protection diode was dropping about 0.2V giving 3.55V and the low drop-out (LDO) 3v3 regulator appeared to be dropping nothing. This was not very promising as the board should run at 3v3, given the presence of the regulator. Time to warm up the hot air pencil and iron then perform some surgery.

Modified PIR

Modified PIR

I first removed the regulator, and consulting a data sheet for the pinout, shorted the Vin to Vout pads where the regulator used to be. You can see how I did this in the before and after shots in this picture. Powering it up from the same source I checked the voltages but found it was performing exactly the same cycling of off to on all the time. So the cycling problem was not the regulator struggling with the low voltage. The voltage on the board side of the protection diode now measured 3.55V so given that PIR detector draw crazily low currents it should be working. But wasn’t. Given it was not looking very promising but I could not figure out why I removed the protection diode and placed a short across those two pins. Completing the modifications in the pictures. Now It worked fine exactly as it had done at 5V but now at 3.7V. So these were the mods that were needed to make the units I have functional at 3v3. Given the strange results we had been getting I hooked up the board to my bench PSU and an accurate multimeter and set the voltage for a real 3v3 and also took the board down to 2.9V in both cases it worked fine. So the issue had not been the actual voltage level as such. I can only think that there is insufficient capacitance across the power rails on the board and at low voltages the turn on/off glitches were enough to re-trigger the detector. Odd, not seen this problem before, but there you go.

In summary a nice little unit, very cheap, hours of fun can be had with them in your projects, watch out for the self re-triggering and it will work comfortably down to 3v3 if you remove the regulator and diode, then short the correct pads to make a straight through path for the supply voltage.

The Hunt for J5

Pi Zero J5 Connections

Pi Zero J5 Connections

J5 is alive, and is definitely not called johnny or a robot in a kids sci-fi film. J5 is the mystery connector footprint on the bottom of the Pi Zero. I have been puzzling over what it was intended for since getting my Pi Zero from Pimoroni.  Asking around amongst those who would know more than me about it (Not difficult to find) the hot favourite was a JTAG port but no one was entirely sure and there was no pinout. An extensive google around was surprisingly information free.

Time then for some reverse engineering, first stop was a USB microscope and a look see for obvious pin functions, gotta tackle the low hanging fruit first. Taking pin 1 to be the pin nearest the J5 ID we can see the footprint is for an 8 pin connector and the body or screen is not connected. 1 is the Pi system reset or run pin as it is labeled, 4 and 7 are ground connections. OK that leaves 5 pins to go. I visually traced the connections and lost them in to the maze of CPU via’s. As other than the reset they did not go to the GPIO pins I could rule out an easy hit as to what they were. The up side is if they were JTAG, it would have to be dedicated pins, not GPIO pins, and therefore projects could be debugged even with a phat in place. Hmmm what were those other 5 pins for. Normally at this point I would start on in with a multi meter or a scope and see what I could find out next. But serendipity smiled upon me, in that way it never normally does.

B+ J5 Connections

B+ J5 Connections

Putting some time into a side project (building a Graphite graphing server) I was working with a Raspberry Pi B+. Purely as I tend to mostly use Pi2’s now and was using up any older ones that were lying around. Embedding them irretrievably into other things. Fiddling with the board during one of many mental luls, I noticed the same mystery footprint on the board directly under the HDMI video connector. In fact it is so much the same it is also labelled J5. Cross referencing the ground pin outs that we know from the Pi Zero we get a match. What is more the 5 pins we had not identified are broken out to pogo pin pads bang next to the footprint. All along with nice labels. Combining the data we have then gives us the following table:-

J5 Pin Information
Pin No Pi Zero Function Pi B+ Function Comment
1 Pi System Reset ? Pull low to reset the Pi
2 ? TRST_N TAP Reset pull low to reset the TAP
3 ? TDI Test Data In
4 Gnd Gnd Signal Gnd
5 ? TDO Test Data Out
6 ? TMS Test Mode Select
7 Gnd Gnd Signal Gnd
8 ? TCK Test Clock

Some further technical info on TAP & JTAG can be found here worth a look at to illustrate some of the concepts behind JTAG. OK, all well and good, what is left to do, identify what sort of connector J5 actually is and make up a JTAG lead for it then connect it up and see if we are right.

Inertial Logger Prototype

Prototype Inertial Logger

Prototype Inertial Logger

The prototype hardware for my inertial logging project is built. Lovely you say, looks nice, fits in a small tin, and just like everyone else, you immediately follow it with “What does it do ??”.

This project follows on from a bunch of discussions in the SHHMakers mailing list. Basically the idea is that you can record or log a track that the tin has followed using only sensing of the movement of the tin. The movement of the tin is the inertia bit. Everything has inertia and sensors that can measure that can also infer how much and by how far something has moved. Inertial guidance works on the same principles and is used for quad-copter pilot electronics etc. This is the point at which, like everyone else, you interject “I just use my phones GPS”. But what about those instances where there is no GPS signal. Try Caving, UrbEx, SCUBA Diving, or just simply finding your car in a multi-story, when you have forgotten where you parked it. Maybe you want to know where the tube system really is under the map of a city rather than the schematic map most underground systems give you. These examples are where inertial navigation and logging have a part to play.

“OK” you say “I understand now. how do you do it ?”. If you put on a blindfold and someone manoeuvres you along a track you can, if you concentrate remember it, this is the logging bit. Each time you are turned this way or that you can feel being turned, this is what a gyroscope measures, rate of turning. If you are moved quickly or slowly you can feel that too, this is what an accelerometer measures, rate of acceleration. If you are in a lift as well as feeling the acceleration, you can feel the pressure on your eardrums change as you go up or down, this is what a pressure sensor measures. You can feel if you are outside or inside by temperature changes, this is what a thermometer measures. People who are blind are more sensitive to these things than the sighted, purely as they use these clues to navigate in a world they cannot see. They also count steps. I don’t think this project will be sensitive enough to count steps but maybe it will. It certainly can measure the passage of time against acceleration/rotation and therefore infer distance.

Zoom in to see the contents of the tin

Zoom in to see the contents of the tin

“So what’s in the tin?”. You are bored with explanations now and want to know about the techy bit. If we zoom in to the tin, we can see a 10 DOF inertial navigation board (GY-87) top left. Under that on the left is a micro SD card. In the middle is a Teensy 3.1 micro-controller. At the right top there is an Adafruit Power Boost 5oo Charger. To the bottom right is the coin cell battery backup for the Teensy’s RTC (real time clock). Underneath the board is a 2.5Ah LiPo. The power boost, LiPo and teensy were bought in from our local supplier Pimoroni. The 10 DOF (degrees of freedom, or number of things it measures) board came directly from china via AliExpress. The power supplying arrangements are a compromise that niggles somewhat. Whilst the LiPo has plenty of power, all the other components actually run at 3v3. the conversion from 5v to 3v3 is done locally on the boards using linear regulators so we are wasting nearly as much power again as they draw. Unfortunately linear regulators dump the surplus energy as heat, far from ideal in a closed tin. Particularly where we want to be able to measure the temperature as part of your logging. Altogether though an adequate first pass for prototyping and testing purposes. There is a bit of a learning curve to be climbed and this is a reliable way to do it. The 10 DOF board has 3 axes of Magnetometer, Accelerometer and Gyroscope on-board as well as an air pressure sensor for us as an altimeter, giving the 10 things or DOF it can measure.

“If you were doing this again what would you do different ?” you ask. Well bearing in mind that I acquired the parts for this a bit back and they have been gathering dust the purchasing decisions would be different. I would be replacing the hand wired SD card holder and Teensy with a Pi Zero. But have to add an RTC. Also I would get rid of the linear regulator on the 10 DOF board and power it form the Zero’s 3v3. Just to move the self heating away from the air pressure sensor which relies on an internal temperature measurement for air density compensation. I would probably add a press button on the outside of the case so that way-points or events could be marked in the track log. Useful for overcoming cumulative errors. One last thing, inertial navigation chips and managers are a field of rapidly advancing technology, many of our smart phones already have them inside. The inertial sensor chips themselves are becoming ever more integrated placing it all on one chip together along with local processing to make them ever more accurate. So something to watch out for and periodically check the current state of play.

The firmware for this prototype is available from my git hub repository https://github.com/AndyKirby/Firmware/tree/master/InertialLogger please note it is a work in progress rather than a finished item.

Salvaging Lead Acid Batteries

Working on a previous project to make a prototype Pi UPS I pulled a number of salvaged lead acid batteries out of the scrap bin.

Battery Resuscitation through Desulfation

Battery Resuscitation through Desulfation

It quickly became apparent that the batteries were all flat and as each had a terminal voltage of around 0.5V they appeared to be beyond life ever again. Not surprising considering the number of years they had lived in the scrap bin without ever having a charge.

Initial attempts to put a charge into them and get them going again were without success. Even over voltage-ing them a little to get them started failed miserably. The best of them was taking around 10 micro amps. After leaving them on charge for 5 days or so the situation had not improved. So what were we looking at ? Maybe they had dried out, maybe the plates had fallen apart and were now mush or maybe being overly discharged the plates were caked irretrievably in insoluble hard lead sulphate crystals.

There are plenty of miracle cures for dead lead acid batteries and desulfation. Frankly I am rather sceptical of most of them. But for some reason I thought although slightly implausible desulfation was a fun hack to try. Chemical means to reverse the crystal build up were out as the batteries are sealed units. So it was time to rummage through the internet for ideas and then hit the scrap bins again for parts. The circuit I settled on is here Pulse Desulfator Doc. This formed the basis and the prototype as shown in the photo was a derivation of this.

Having nothing to loose other than a bit of time constructing and debugging it I set too to build it. The inductor was a hand wound approximation, the logic inverter shown in the schematic was replaced with a simple transistor based inverter using a 2N2222 NPN transistor and the mark space ratio of the 555 astabel circuit needed adjusting. Probably because the inductor value was a touch lower than it should have been. But in the end it appeared to be working.

Now the acid test (see what I did there….). From the picture you can just see the ammeter on the bench PSU showing the battery taking a charge of 200 milli amps. So success. It took 2 days of float charge plus the desulfator pulsing away to get this recovery. Over this period the input current could be seen steadily increasing, whereas before with a stable DC supply it had just sat there and done nothing. The open circuit voltage of the battery at the time of writing now shows 4.5 volts so there is a way to go yet. It could be a couple of weeks or so before the battery is as recovered as it ever will be. In reality I can’t see them ever being “as new” however a trick worth knowing about and trying when salvaging neglected lead acid batteries.

Not to self if trying this with an old car battery check the electrolyte levels first and be prepared to except that the plates could just be mush and the battery beyond recovery.

Prototype Pi UPS

After advocating for a while that it is worth running up services on Pi Servers one at a time as needed. It occurred to me that we have no UPS to keep them going when the mains electricity drops out. We also have no way to prompt services to shut down in an orderly manor under the same circumstances. This gets to be more critical when we are running infrastructure services like RfID door access and a space automation MQTT broker.

An uninterruptible power supply for the Raspberry Pi

An uninterruptible power supply for the Raspberry Pi

Being as I am also running similar services at home I needed a similar solution for home. Sounds like a call to hack then, first stop was the junk and scrap bins, then a quick rummage through the spare bits left over from Chinese AliExpress shopping trips.

I found an ex UPS maintenance free lead acid battery that had sat in the scrap bin for too many years and a couple of these tiny 3A SMPSU DC-DC switcher modules that are incredibly cheap. The SMPSU modules can cope with up to 28V input and the output voltage is set by a small potentiometer. I also found a scrap laptop PSU that had a decent current delivery at under 24V. All in all the most expensive bits were the screw terminals that you can see from the picture I used to make conections to the board.

Lead Acid batteries have the useful property of being low maintenance and they will take a float charge providing you supply them with a constant voltage at the maunfacturers reccomended value. They will sit there on this float charge for as long as the battery will live. So after a quick rummage on the internet the first switch module was adjusted to provide a constant voltage at the manufacturers reccomended float value of 6.85V for the battery shown. The battery and input to the second switch module were conencted in parralel across the output of the first switcher. The ouput votlage of the second switcher was set to the 5.1V that is best to feed Pi’s with.

That then was the prototype UPS finished. When the supply to the UPS fails the battery takes over and supplys the Pi. When the mains supply comes back on the battery goes straight onto float charge and the Pi is running from the mains. Providing that the battery float voltage is less than the supply voltage and the Pi voltage is less than the battery voltage it all works. At 6V these thresholds are all a little close together and the UPS could do with a 12V battery and then adjusting to charge at that voltage instead. But this does work and the concept is proved.

The next task is to scale this up to run a whole shelf of Pi’s, with a mains high current SMPSU to drive the float voltage and supply the Pi’s, a salvaged car battery for the uninteruptible bit and one of these cheap tiny DC-DC SMPSU’s per Pi. But that is another article for another day.