Using pulse width modulation scheme for LCD back lighting an app note from Hantronix. Link here (PDF)
LED back lights on LCD modules are generally driven with a dc voltage through a current limiting resistor. This simple approach is perfectly acceptable for most applications. When the primary consideration is an extra bright display, the lowest possible power consumption, or a back light that can be controlled over a very wide brightness range another method is needed. The purpose of the paper is to describe this method.
We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:
- Yes, we’ll mail it anywhere in the world!
- Be sure to use a real e-mail in the address field so we can contact you with the coupon.
- Limit one PCB per address per month please.
- Like everything else on this site, PCBs are offered without warranty.
- PCBs are scrap and have no value, due to limited supply it is not possible to replace a board lost in the post
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The Raspberry Pi is a very capable device whose hardware has been pushed to the limit in all sorts of interesting ways. But even the most ingenious of experimenters have to agree on one point; it doesn’t possess an analog-to-digital converter. If you want analog inputs you will have to buy or build them.
[Mincepi] has done just that, but not as you might expect by adding an integrated circuit on one of the Pi’s interfaces. Instead the circuit [Mincepi] is using consists only of passive components, measuring the time taken to discharge the parasitic capacitance of one of the Pi’s inputs from logic 1 voltage to logic 0 voltage through a resistor into the voltage to be measured. This is a long-established approach to A to D conversion, one that was achieved back in the day with purpose-designed timers as microprocessor ancillaries.
The problem is that the Pi does not have a timer peripheral, so [Mincepi] has used the shift registers that form part of the Pi’s SPI and PCM inputs to perform this task on two channels. A sample rate of 100kHz and 6-bit resolution is claimed, with enough voltage range for a 1V peak-to-peak audio signal to be sampled.
Of course, simplicity does not guarantee a good ADC, and this circuit does not perform very well. It is noisy, non-linear, and as [Mincepi] puts it, probably sensitive to temperature. And though [Mincepi] talks in detail about the software to drive it, none is forthcoming. To quote: “It doesn’t include code since I’m in the process of writing a proper sound device module. My previous code was a simple character device, but it worked just fine, and served to prove the concept.”
We really want this to work, even if it’s not the best ADC ever. So we eagerly await the sound device module, and look forward to more news from the project.
This may be the simplest of simple ADCs we’ve yet featured here on Hackaday, but it’s not the first we’ve seen. There is this one using a comparator for example, or this one using a flip-flop. It is the essence of creative electronics to eke a function from a component that was never meant to be, please keep them coming!
Filed under: hardware
, Raspberry Pi
For over the normal range temperature, Hantronix presents a simple temperature compensation circuit to correct LCD contrast, Link here (PDF)
The optimal contrast setting for LCD displays varies with ambient temperature. For most applications this variation in contrast is tolerable over the “normal” temperature range of 0°C to +50°C. Most Hantronix LCD modules are available with an extended temperature range option which allows the display to operate from -20°C to +70°C. The changes in contrast are NOT usually tolerable over this wide a range of temperatures, which means a way of adjusting the contrast voltage as the ambient temperature changes must be provided.
As the temperature decreases the LCD fluid requires a higher operating voltage in order to maintain a given optical contrast. One way to provide for this is to give the user control of the contrast. This is a simple solution but quite often its not desirable or practical.
We are moving forward on the first instance of a Distributive Enterprise – with the D3D Business Plan – a vision for innovation in the field of economics. The innovation lies in discovering a mechanism to displace factory production with social production, due to the benefits mentioned in the Executive Summary of the Business Plan –
The proprietary economy based on protectionism and competitive waste produces consumerism and is a threat to human creativity, progress, and autonomy. Our value proposition is substitution of factory production with more efficient social production. This involves substitution of proprietary production with open source social production by educating and involving the end user in the production process. This empowers individuals to build skills and to build the world around them, as humanity transitions to more integrated human skill sets than those characteristic of the industrial revolution. Moreover, this paradigm shift introduces the possibility of lifetime design, where users are capable of fixing their own products because they built the products themselves.
One condition for success is attaining Viral Replicability Criteria:
There is a lot of work that goes into this, but the scaling potential looks good on paper. Nearly 1000 3D printer builds in one month would make this into a decent 3D printer company about the size of Lulzbot– except all the wealth is being distributed to the numerous people running the workshops:
Is it really possible? To create a virtual $10M 3D printer company without employees in a year’s time, where collaborators run the world’s first significant open hardware company as a swarm? A federated WordPress or such – but done with Hardware? What are the things to consider beyond some of the key elements in the Viral Replicability Criteria? Clearly there is a number of standard business functions that must be covered, and the challenge is to address them in a distributed and distributive organization. Standards, education, and certification will be key – and as an education nonprofit, it appears we are well-positioned to fit that role with OSE.
Nobody has tried out the Distributive Enterprise concept yet – so we are in pioneering darkness – thought it seems obvious to me that such a model can produce unprecedented results of viral odoption. Since we are giving it all away – perhaps that’s the reason why nobody tried it before.
There are already 3 people interested in replicating the One Day 3D Printer Build Workshop in their home towns – so we are on track so far. We will just have to see how the first workshop turns out. This is a direct invitation to True Fans and other dedicated open-sourcers to take this as an opportunity to change economic history.
Atmel’s application note (PDF!) Using the Master SPI Mode of the USART module:
• Enables Two SPI buses in one device
• Hardware buffered SPI communication
• Polled communication example
• Interrupt-controlled communication example
For the majority of applications, one Serial Peripheral Interface (SPI) module is enough. However, some applications might need more than one SPI module. This can be achieved using the Master SPI Mode of the devices with this feature such as Atmega48.