Blog - page 7
Its easy, if you ask me!
I was apprehensive before my current project. But no longer. I do not have many photos, but will edit once I have them.
This is a highly involved project!
This is a series of post I am planning to write on projects I am doing, and my learnings from them.
Li-ion charger ( see here http://www.ebay.in/itm/TP4056-5v-1a-Lithium-Battery-Charging-Module-lipo-lion-charger-mini-USB-port-/171827715868?pt=LH_DefaultDomain_203&hash=item2801badf1c)
A Li-ion battery, choose a 1200mAh+ battery for a good amount of backup. Mostly these go for 100/- at Lamington Road.
An Arduino ofcourse, but any microcontroller with a spare ADC pin will suffice.
A couple of resistors, I used 10k and 39k 5% resistors. These are used to create a voltage divider network which senses battery voltage. Dont spend a lot on 1% MFR resistors, it is possible to have accurate results in software.
A switch with three pins, one common, two inputs. this is used to seperate the battery from the arduino into the charger and vice versa.
Firstly, your Arduino can get permanently damaged if the ADC input voltage is greater than the supply voltage.
A Li-ion battery highest voltage should not cross 4.2 volts. Its full discharged when it reaches 3.3V. Effectively, our ADC has to measure this range for the Arduino to know how far along will the battery last.
Here is what has been connected.
TP4056 Bat+ to one extreme terminal of switch.
TP4056 Bat- to Battery Negative terminal
Arduino 5V pin to other extreme terminal of switch.
Arduino GND to battery Negative terminal
40k and 10k resistor divider between battery terminals. 40k Resistor connected to Battery positive, 10k to battery GND
Center junction of voltage divider connected to A0 on the Arduino.
Center pin of switch connected to Battery (+) terminal.
Okay! I hope you have drawn a good circuit, please verify again.
One flick of switch will disconnect battery from the arduino and connect it to the charger, the other flick will be vice versa.
The TP4056 has two LED's, Red is charging, Blue is Charged
Change the ADC reference to Internal 1.1 V, see here https://www.arduino.cc/en/Reference/AnalogReference
At 4.2v, the A0 pin should ideally see a voltage below 1.1v, about 0.84 volts. This is the premise to choose those resistor values. With the 1.1v reference, this should be easily measurable.
Use the AnalogInOutSerial example, in the Arduino IDE, Change the ADC reference in the setup function, and note values. Lets say it is 650, this is ADC count. This has to be converted to voltage.
A0 pin voltage= 650*1.1/1023=0.69V. With expected 100% accurate resistor values, the battery voltage should be 3.38V( I leave this as an excercise for the reader)
Measure the Voltage of the battery. Lets say its 3.34V.
Why is there this difference? Because
1) The 1.1V reference is not purely 1.1V
2) The resistor values are not exactly 39k and 10k.
We add correction to this now. Charge the battery, and then let it discharge. Measure a couple of these ADC and Battery voltage values, and find the average multiplier to be provided in the calculation. For our example above, the multiplier is (3.34/3.38)=0.988
You now have the correct battery voltage
Battery voltage= ADC reading * 1.1 * multiplier * ( sum of resistor values)/1023;
Problems that can occur while running on batteries
1) Batteries will drain.
2) The Atmega chips have a certain max clock speed at which they run at different voltages. the datasheet will tell you this voltage speed relation. This means that unless you have a very stable voltage, a very strict timing cannot be achieved, because the system clock can be not so accurate
3) Brown Out- If the battery dips too low, the system will reset itself, can be mitigated by changing a couple of fuses.
Jig and guide for a circular saw
Mini project: To build 2 jigs or guides for the circular saw.
The base or plate of the circular saw is a rectangular piece of metal, which is square. It exists to ensure that the saw cuts exactly at 90 degrees into the wood. This is one type of guide which is built into the circular saw. What we require to build is a guide to help cut in a straight line without having to constantly measure how far from the line to setup the guide.
- Assume that the base plate of the saw is 4" wide. The blade will spin ~1" from one edge and ~3" from the other. It is very, very rare to cut using the 3" side since this side has the motor mounted on it. But in a cramped space when the saw can be applied only from one direction, I have found that using the 3" side is safer that pulling the saw toward the body.
- We will make this guide 4' long. This will cover the 8'x4' sheets that we are always going to be working with.
- The guide has 2 pieces glued and screwed to each other. screws are optional and infact not recommended. These are used simply to hold the pieces together while the glue dries. The 2 pieces are the base and the fence. The edge of the base is held on the line on which we are cutting while the fence is used to guide the base plate of the saw in a perfectly straight line.
- Cut the fence from a sheet of 1/2" mdf or particle board or what ever you have at hand.
- Cut the base from a sheet of 1/4" material.
- Glue the fence onto the base in the manner below. Before gluing read step 7. Based on the position the fence on the base in such a manner that the circular saw will have something to cut out.
- Once the glue is dry. Using the circular saw for which the guide is being made, cut the base by placing the base plate against the side of the fence, this will give a 0 tolerance cut for this side of the circular saw.
- Do the same thing for the other side of the circular saw.
- This guide and the circular saw are not a couple. </ol>
- Draw out the line that you wish to cut along
- Place the guide such that the edge of the base is along the line.
- Clamp the guide from both side.
- Let her rip!!!
- Remember to always cut on the waste side of the line. This is where a guide which can be setup for either side of the plate comes in handy.
This guide is used to make straight cuts which are not necessarily at 90 degrees to the edge.
Now go forth and make
We have finally begun THE series of builds of storage cabinets in the asylum. If you've been to the asylum then you know that the number of tools has suddenly shot up. Members too have begun using more than just the electronics equipment and we are now increasing blah blah blah .. go read Storage cabinets for carpentry and Mechanics. If you haven't been to the asylum then stop reading and get to the asylum now
We met at 12:30, the gang from the second carpentry class and Kapil. A poor turn out in my opinion, but the torrential rain in the morning may have been the reason.
I explained the build, the purpose of a build group and the series of builds we are going to be doing with particle board. In another few months the transformation of the asylum is going to be complete.
This specific build is a storage cabinet for carpentry and mechanics tools. I broke down the storage cabinet design into 5 parts
- Column 1: Karthik, Aarudra, Kapil and Mohammed
- Column 2: Karthik, Aarudra, Kapil and Mohammed
- Drawers: 4 in total, Rushneh from my knocking on wood class will take this up with a couple of colleagues.
- Pegboard: Unassigned
- Collapsible table: Sonia from the knocking on wood class again.
In true build group fashion, each person or team is responsible for completing a portion of the build. The build members can meet at anytime at the convenience of the teams. The only limitation is that Kartik or myself needs to be present when the power tools are being used.
On the first day the team for column one used the jig saw, circular saw and a couple of make shift guides and long power cords to chop up the 8x4 11mm sheet of particle board into 2 sides of the columns. The big 'b's if I may ;)
4 sheets of particle board have been provided by Associate Decor Limited (http://www.associatedecor.com/)
- 2 11mm boards
- 1 8 mm board
- 1 17 mm board
Particle board cuts up as easily as MDF, infact it might be a little easier since it is a little less dense. In the next post, I'll probably show you how we made the guides for cutting straight lines across 4 feet and some tips and tricks on how to screw into the edge.
If you wish to contribute to the build, get in touch with me on facebook. The pegboard portion is still unassigned.
The first 2 sessions of the carpentry class have gone by so quickly I've not had the chance to "report" about them before this
Over the course of Knocking on Wood I, I learnt a lot about teaching woodworking; probably more than my students.
This time I have tried to reduce the shortcomings.
- The course commitment is too much, 4 Saturdays is a lot. The current class is 3 Saturdays long
- I've moved the entire format around. Introducing practice time even earlier than teaching about tools and grain.
- Actual working time has been increased so that the time to correct mistakes is larger.
The participants for this carpentry class are as varied as the first, education-ists, environment-ists and non working-ists; all wish to learn.
One thread runs through this group and with the previous one; my jobs are too small, no carpenter will take up my designs, home repair. All these 3 reasons are perfect; to me its the beginning of a revolution. Ofcourse 16 people will make a really, itty bitty revolution, but hey a rolling ball of snow can begin from a bitty pebble.
Last week, 7 participants and I got together in the asylum for the first session of the carpentry class. This time after a quick round of introductions and some ice breaking, I went straight for sawing and chiseling out bits of wood.
The task was simple, fit one piece into another in various ways. The learning from the exercise is massive; I'm definitely going with this exercise in the future. It is easily the only task that needs to be mastered to be a master woodworker; You learn
- Measuring and marking: This sounds so trivial, but I know 16 persons who will take a chisel to you if you say this is easy.
- Cutting with a saw: After marking, you had better cut on the correct side of the line; Sigh! yes there is a correct side. Come for a class and you will learn.
- Chopping with a chisel: The final stage of any thing is taking out the waste. A chisel is accurate and neat and practice makes perfect.
We ended carpentry class 2 session 1 with a talk on tools and grain. I felt this was much easier to grasp as the hands on time had given enough context.
Carpentry class session 2 began with joints, and then the design of the laptop table.
Interestingly, 2 members of gang II decided to change a few parts around. One will build a "tablet table" and another is building a tools trolley. Using all the same number of pieces and simply moved a few around, voila a new item of furniture.
Ahh, I so love building with wood.
Day 2 ended with the completion of the frame for the table top. That's the big one; 4 joints, 8 chops, 16 cuts.
The accuracy of the joints created was a kind of vilification of the time spent in practice.
All in all a great first 2 sessions of carpentry class.