Archive for the ‘projects’ Category
One thing that all us need know is that the project power requirements not only besides on efficiency and quality. Efficiency and quality are subjective terms and you (like me) break and open some market products, you’ll found some really dirty way to power up a electronic device.
Well, with that in mind I’m working in power my Samsung Infrared Decoder with a transformerless power supply. Transformerless Power Supplies, instead of use regular transformer-rectifier circuit or switched power circuitry, use direct coupling of AC line to passive components, like resistors and capacitors, to obtain a desired voltage. Yes, it’s a very dangerous idea, but you can control it and minimize risks too.
Some projects are really cheaper, and don’t require much power. Think in a microcontroller circuit that do the following things:
- Wake-up from sleeping;
- Reading temperature (ADC);
- Transmit it (802.3.15.4);
- Return to sleep;
These steps doesn’t require more that 20mA (aprox), and most market components are cheaper. But if you want to really make this cheaper and smaller, a transformer/wall adapter supply it’s a big monster. The bad news is that transformerless power supplies, not only are dangerous but less current capable of other supplies. If you need more than a few mA, your circuit will be exposed to a great risk.
The two basic types of transformerless power supplies are resistive and capacitive. You can view nice example after Google it. My idea it’s use a capacitive version. My circuit simulation is based on bellow (ignore V2 for now, I’ll explain it later):
The main rule to keep in mind is that “R1” and “XC1” (capacitive reactance) are the only input current limiters. So, more current, need other values. The other rule is to keep the supply working: keep output current requirements less than input current calculated. See:
We need to resolve the input voltage in terms of RMS (Root Mean Square) value. The voltage is the RMS value of a half-wave, because D2 rectifies it. So:
Put all it together to resolve:
I’ve chosen values to meet approximately 5V@20mA. The RMS voltage value in Brazil is 127V. The frequency is 60Hz. The zener used have 5.1V drop across.
For circuit simulation I’ve used MacSpice, a great Berkeley Spice 3f5 clone. In this circuit you view another voltage source (V2) with zero voltage output. That’s a way to measure output current on transient analysis on Spice. You can download my circuit file for run your own simulation here. The results are:
The voltage drop on zener diode and common diode D2 is determinant for output voltage. In really, I never reach desired 5V output because of voltage drop across D2. But it’s ok, most modern microcontrollers operate on a wide range of voltages. The output voltage is given by:
The next step is test a real circuit with real load. So long I’ve news, I’ll post them here.
Remember again that transformerless power supplies are naturally unsafety. After decide make that circuit, and finish it, you have in your hands live AC voltage very close to low power electronics, with is a great danger. Stay as advised.
Well, I can’t finish the PCB for this project yet (I’m planning make it with a Transformerless Power Supply), but I’m posting the Microchip C18 code for all that want work with this protocol.
Please, visit my download page.
I had ear some time ago that laziness sometimes is the best thing for inspiration. That week I discover that’s true. Some nights, I lay on my bed to watch some thing on TV and doing some electronic research, before sleep. And, I don’t like to put off the lights (effficient ilumination is the best friend for a good reading) . Then, obviously, before sleep, I need to stand up to turn lights off. At my side, on bed, always resides a great remote control TV, with a set of unused buttons, telling “use us to turn the lights off“.
That’s a project that I was retarding because other, but now I decide to initiate and finish it.
The Basic Idea
The first step is recognize what my remote control is send to TV. It’s a Samsung remote control, with TV, VCR, DVD and STB specific and shared functions. My basic idea is: use some of this unused buttons to turn the lighst ON and OFF. But, why not dimmer the lamp? Why not doing some other useful thing? (Yes, thats because some projects growing up…)
So, the basic idea now is:
- Make a device that recognize when a command is addressed to it self or not;
- Recognize different commands;
- Save usuful states (dimmer regulation);
The Internet has a lot of information about RC5, NEC and Sony IR protocols, but not the same for Samsung. After some search at Google, I found this usefull page with some information about Samsung IR protocol. Resuming Samsung protocol:
- 37.9KHz carrier wave (ON state is a burst of carrier with some duration, OFF is absense of it);
- 1 Start bit (4.5ms ON, and 4.5ms OFF);
- 32 data bits stream (data + address?);
- bit “1” (590μs ON, 1690μs OFF) (thanks to Islam qabel, for the more precise bit duration);
- bit “0” (590μs ON, 590μs OFF);
- 1 Stop bit (590μs ON, 590μs OFF);
I think that more information only with a test.
The test circuit is very simple, consisting on a IR receiver (with filter, carrier demodulation and output). My only device available at home is a TSOP2236. Well, let’s go see what hapens.
TSOP2236 is a dedicated IR receiver with PIN diode and preamplifier, assembled on lead frame. The epoxy
package is designed as IR filter, to improve sensibility. The demodulated output signal can directly be
decoded by a microprocessor, but it’s logical reversed:
- ON state (carrier presence): TSOP output LOW;
- OFF state (carrier absence): TSOP output HIGH;
To make measures and confirm my suspects, I had use my Logic Analyzer from Saleae on the follow circuit:
That’s the results for press button “1”:
The process to gathering all this information is very easy with Logic Analyzer. The measured times differs a little bit, but this isn’t a problem. I count the transitions after the START bit and there’s 32 bits in.
Look again at the sequence of high and down states. Remember that we have a reversed version of the original IR wave from remote, because TSOP OUT signal is inverted. But actually it’s really doesn’t matter. What I need is: pressing “1” differs from pressing “2” or other buttons on remote. I don’t wanna to create a compatible device.
Decoding the data stream
To decode the data stream I used a PIC18F2520 MCU. I already has working on 16bits and 32bits MCU, but this project is much simple to require a great MCU. My design goals are:
- Use internal clock (8Mhz, Instructiom Time TCy = 4/8MHz = 500ns);
- Use Timer0 as counter with 1us increment (Timer0 prescaler to 1:2);
- Use External Interrup 0 (INT0) to handle incoming IR waves and get the building IR code (final version);
That’s the circuit:
The code (for Microchip C18 compiler) consist in a set of functions to detect when the signal change it’s state from DOWN to UP or UP to DOWN. See the sequence (basic):
Note that for data bit identification, only HIGH time is important. It’s the difference between logic “1” and “0”, so you don’t need to be very precise in that differentiation. The red right program branch, needs to run 32 times, for all 32 bits.
The test was a success! After all, I have a 32bits unique data, that contains (probably) a Address Part and a Data Part. Again, I don’t worry about what is address or data. Only need unique 32 bits codes. If address part repeats (because you are send codes to one device), data should be unique. Ok to me.
The stream is read as it is delivered from TSOP to MCU, from left to right (START BIT to right). I’m considering from LSB to MSB, so when you see the analyzer stream signal, you are viewing the reversed version. See:
After some nights adjusting some things, the code works great! I’ll publish it here in the next week.
As I think, some codes changes if you are using TV, DVD, VCR or STB buttons. See the codes for VCR function:
If you observe the first pictures, about button “1” stream, you can see the sequence of 1110000 (reverse order, 0x07).
Proof of concept
To test my concept, I programing the device to waiting VCR signal functions (ended with ….0505) as you can see:
- Buttons 1,2 and 3 turn ON color RED, GREEN and BLUE;
- Buttons 4,5 and 6 turn OFF color RED, GREEN and BLUE;
- Button 9 turn ALL ON;
- Button 0 turn ALL OFF;
- VOLUME+ increase LED power (PWM duty cycle);
- VOLUME- decrease LED power (PWM duty cycle);
See my video:
Now I need to design a transformerless power supply and the power control circuitry (TRIAC, etc) to control the real lights. Some nice ideas to next version:
- Store dimming states on internal PIC EEPROM, so you can save desired conditions every time;
- TV Remote now can act in others projects too (robots, toys, other home automation, etc);
- With a small LCD, create a small menu, some configuration options, to more advanced projects;
I hope yours enjoy this project. From the first paper to here, I took one week to get it working properly. In a few weeks, I’ll share all the files here, in downloads page. Thank’s!
For who need SH1101A OLED driver, I’m posting here my code (written in Microchip C18, but easly to port to other platform) to help more people on get use this great OLED display. It’s not finished, yet, but it’s very useful.
The code has geometric draw functions to draw single pixel, lines, rectangles and circles with fill option. There’s characters output functions too, with 8×6 pixel font.
The icons for Battery (animated), Bluetooth, WiFi, Sound (animated), etc are on the code too.
Some example of available functions are:
- SetPixel(), GetPixel();
- Character output functions, PutROMString(), PutString();
In the code you’ll find a DS18B20 Dallas OneWire Digital Temperature sensor driver too. That’s a limited version (only work for one sensor in OneWire bus) but works great. You get a float reading plus a string with temperature value (in Celsius Degrees). More improvements coming soon.
Well, let’s go to download link:
If you have any trouble with that code, email-me or let me a comment.
Some people ask me about how to do hand soldering on smaller parts, like on my OLED Display Board. It uses a “TAB” (tape automated bonding) or “COF” (chip on flex) style flex tail mated with a “COG” (chip on glass) display. Normally, TAB connector is soldered directly to corresponding pads on your PCB using a hot-bar soldering machine.
I don’t have that hot-bar soldering machine, so my hand’s can make the job. The first time I’ve done this soldering, I was a bit scare about damage the connector. My only tip is “don’t spend much time over the fragile contacts.”
For help us, I’ve recorded my last OLED soldering. Maybe can help some people about SMD soldering (as some internet videos help me some years ago).
Someone send to me a question, about how much current my OLED board consumes at all. Well, after measure with a multimeter the answer is: 660μA (aprox.) with display all ON and contrast at 0xFF (max). But this question make me thinking about how measure that current myself, without a multimeter.
When I’m in graduation (some good years ago) I made a little circuit to measure how much current my power supply project output. The circuit is based on “high-side current-sense” methodology. See my hand-drawn circuit above:
This circuit is a classic high-side current-sense, where the voltage drop across Rs resistor is isolated by a operational amplifier (op amp) in a differential configuration with unitary gain. The many implementations of technic were based on discrete components or semidiscrete circuitry. In their simplest form, such high-side monitors require a precision op amp and a handful of high precision resistors.
The resistor value should be low (like mΩ scale), to minimize power losses, but don’t be too low, because stability problems. And don’t forget about power dissipation across the resistor.
One common approach for high-side measurements has been the use of the classic differential amplifier, which is employed as a gain amplifier.
So, after reading a lot of theory, I’ve going to search my integrated differential amplifier.
Integrated Differential Amplifier
- Tiny SOT23-5 package;
- Low cost;
- 3 gain options (20V/V, 50V/V and 100V/V);
- +2.7V to 28V range of operation;
- Consumes only 30μA;
- 0.18% full-scale accuracy with 100mV Vsense input (This is equivalent to only 0.18mV input offset voltage);
The MAX4372, in a tiny SOT23-5 package is a very good device to make a current sense device. You can set the full-scale current reading by choosing the device:
- MAX4372T: 20V/V Gain;
- MAX4372F: 50V/V Gain;
- MAX4372H: 100V/V Gain;
What means 20V/V Gain? If you have 1A current flow through a 100mΩ Rs resistor, you gave only 0.1V drop. But with 20V/V, you multiply this and obtain 2V. Obviously? The design goal with Gain is thinking in terms of full scale design. If your A/D converter uses 3.3V was reference, you can consider this to check what the max current value you can measure with determined gain value.
A test circuit
I’ve designed a test circuit to test my idea. Basically is a MAX4372T with a 100mΩ Rs. I’ve mounted it in universal board, and my idea is connect it to my USB Low Pin Kit:
To test them, I’ve used a PIC18LF2520 and a great character LCD from Electronic Assembly. See my test circuit working:
The pictures show that the global idea works great. Now I need some work to improve stability and other features.
The next step is create a USB device for read, store and show the current measurements:
Some people have contact me about my projects, with questions and support. I’m very happy because when I started blog I can’t imagine that my little stuff has been useful to other people.
And now I like to share my Eagle project files with us:
I hope this files may help you with your design, with your project. If you need some help, email me.
So long I finish some source codes, I’ll post my codes too. I promise! 🙂