Matt Sarnoff wrote in to share his homebrew Ultim809 computer. Based around the slightly unusual Motorola 6809 processor, he’s creating the entire thing from scratch, from designing the circuit to writing his own operating system and games. He’s planning to release the software and schematics for the project when the build is completed, but we want to see them now!

More:

• The MyCPU – Homebrew computer
• Building a CP/M 68k computer from scratch
• Homebrew 68000 computer in the making
• Homegrown modem from days of yore

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This is a viral marketing campaign for some kind of extra-fine point Pilot pen. I love the minifigs themselves, but the campaign bugs me for a couple of reasons: 1) I’ve been Googling around pretty hard and can’t seem to figure out exactly which of Pilot’s many pens these photos are promoting, and 2) nowhere does it explicitly state that the art on the minifigs was actually done with whatever pen they are advertising. So even if I could figure out which one that was, it’s not at all clear that I could actually use it to tattoo my own minifigs. In any case, any kind of super-fine-point permanent maker would probably work. [via Boing Boing]

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The Philips Semiconductors TDA8551 is a small audio amplifier with an integrated volume control. When operated from +5 V, it delivers a nominal output power of more than one watt into 8 ohms. It can also be used over a supply voltage range of +2.7 to +5.5 V, with correspondingly reduced output power. The output volume can be adjusted from –60 dB to +20 dB in 64 steps, using a set of up and down push-buttons. The shared UP/DOWN input for the up and down switches has three states. If it is ‘?oating’, which means that both of the switches are open, the volume remains unchanged. A pulse to earth decreases the volume by 1.25 dB, while a positive pulse increases the volume by 1.25 dB.

When the power is switched on, the internal counter takes on the –20 dB setting. An additional input (MODE) allows the amplifier to be switched from the operating state to the mute or standby state. If this input is held at the earth level, the amplifier is operational. If +5 V is applied to this pin, the TDA8551 enters the Standby mode, in which the current consumption drops from the typical operational level of 6mA to less than 10µA. Finally, the MODE input can be used as a mute input by applying a voltage of 1 t0 3.6 V to this input. This voltage can be provided by a connection to the SCR pin, which lies at half of the operating voltage and to which a filter capacitor is connected.

The loudspeaker is connected in a floating configuration between the two outputs of the bridge amplifier in the TDA8551. This provides the desired output power level, in spite of the low supply voltage. For headphone applications, which do not need as much output power, you can connect the headphone between earth and one of the outputs, via an electrolytic coupling capacitor. You can make a stereo headphone amplifier in this way, using two TDS8551 ICs. The TDA8551 is housed in a DIP8 package. The SMD version is the TDA8551T, in an SO8 package.

This circuit is based on a standard LT1074CT switching regulator IC. For sure, Application Note AN35 published by Linear Technology describes the design far more elegantly than the author could in this short article. Interested readers are therefore strongly advised to get a copy of AN35. The schematic shows the LT1074CT used as a positive step-down or ‘buck’ converter. The ‘switcher’ is used to convert a +12-volt car battery voltage down to +3 volts for use with the personal hi-?’s and hand-held games for the author’s two boisterous children on long car journeys. Note at under ten years of age, children will rarely be hi-? a?cionado’s and are generally not concerned with any noise generated by the ‘switcher ‘circuit.

The circuit is connected to the car +12-V system via the cigarette lighter socket — is advisable to use a fused version of the cigarette lighter plug. The +12-V arrives on the board via screw- terminal block J2. Diode D2 provides a reverse voltage protection, while C3 decouples the input to the switcher IC. The LT1074CT briskly switches the supply voltage on and off in response to the signal applied to its F/B input, to the extent that the average output voltage is at the required level. The values of potential divider resistors R1-R3 have been chosen to attenuate the output voltage so that there is 2.5 V at the F/B pin.

The difference between the attenuated output voltage and the internal 2.5-V reference is used to control the modulation effect of the switcher. Components R2 and C2 provide frequency stabilization for the feedback loop. Inductor L1 along with the LT1074CT form the main switching components, while C1 provides decoupling for the output load. The 3-V output voltage is taken from screw terminal J1. With this circuit built, boxed up and installed in your car, you can look forward to possibly your first ‘quiet’ long car journey.

Today, in 1938, Ernest Gary Gygax was born in Chicago, IL. He would go on to create a gaming and publishing empire, built on math-driven storytelling and gem-like Platonic solids dice (co-creating the pioneering role-playing game Dungeons & Dragons).

Anybody who’s ever played Dungeons & Dragons will know why Gary Gygax is suited to be celebrated in a Maker Birthday shout out. When I first got into the hobby, and oh did I ever get into the hobby, I was penniless, just out of high school. My gaming group and I could barely afford the essential game components. Everything else we made ourselves. We fashioned our own miniatures and dungeon furniture from clay, learning basic ceramics in the process, built our own gaming tables and scenery, learning carpentry and all the basic miniature modeling and scenery-making skills. And, of course, we spent countless hours sketching and mapping out worlds, characters, and epic adventures within those worlds. And that was all before actually playing the game!

It’s staggering to me to consider the impact that Gary Gygax, D&D, and RPG have had on popular culture, the ethos of imagining and modeling whatever world you want, and in the acculturation of generations of nerds who got to experiment with social interactions (from within an accepting tribe) to help them negotiate the wider world of Muggles.

So thanks, Mr. Gygax. You were instrumental in giving us geeks “permission to play,” and in showing us how we could combine our intellects and our interest in math, science, history, and technology, with our imaginations and our ability to render the multiverses inside our heads. Happy Birthday.

In celebration of Gary’s birthday (who, BTW, died in 2008), why not share some of your D&D/RPG stories, and especially, how these games might have inspired you as a maker.

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On many cars, the boot light will not go out until the lid is properly closed. It is all too easy when unloading the car, to leave the lid ajar. If you are unlucky and the car remains unused for some time, the next time you try to start it, the lamp will have drained the battery and you will no doubt utter a few appropriate words. The circuit described here will give a warning of just such a situation. A mercury tilt switch is mounted in the boot so that as the lid is closed, its contacts close before the lid is completely shut. The supply for the circuit comes from the switched 12 V to the boot lamp and through the mercury switch. When the lid is properly closed, the boot lamp will go out and the supply to the circuit will go to zero. If however the lid is left ajar, the lamp will be on and the mercury switch will close the circuit.

After 5 seconds, the alarm will start to sound, and unless the lid is shut, it will continue for 1 minute to remind you to close the boot properly. The 1-minute operating period will ensure that the alarm does not sound continuously if you are, for example, transporting bulky items and the boot will not fully close. The circuit consists of a dual CMOS timer type 7556 (the bipolar 556 version is unsuitable for this application). When power is applied to the circuit (i.e. the boot lid is ajar) tantalum capacitors C1 and C2 will ensure that the outputs of the timers are high. After approximately 5 seconds, when the voltage across C2 rises to 2/3 of the supply voltage, timer IC1b will be triggered and its output will go low thereby causing the alarm to sound.

Meanwhile the voltage across C1 is rising much more slowly and after approximately 1 minute, it will have reached 2/3 of the supply voltage. IC1a will now trigger and this will reset IC1b. The alarm will be turned off. IC1a will remain in this state until the boot lid is either closed or opened wider at which point C1 and C2 will be discharged through R6 and the circuit will be ready to start again. To calculate the period of the timers use the formula: t = 1.1RC Please note that the capacitor type used in the circuit should be tantalum or electrolytic with a solid electrolyte. The buzzer must be a type suitable for use at D.C. (i.e. one with a built in driver).

Via io9, Arizona State University has assembled the highest-resolution Mars map to date, the images drawn from 21,000 pix shot by the Mars Odyssey orbiter’s THEMIS camera.

The maps show Mars as if sliced from a globe, unwrapped and flattened out on a table. Nearly 21,000 individual images have been smoothed, blended, fitted together and cartographically controlled to make a giant mosaic that web viewers can zoom into and scroll around. The few missing pieces show where clouds and poor lighting have thus far prevented map-quality imaging; these places are high on mission planners’ must-image target list.

Interactive zoomable map

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The circuit diagram shows a low-cost 3-input video MUX cable driver. In this circuit, the amplifier is loaded by the sum of RF and RG of each disabled amplifier. Resistor values have been chosen to keep the total back termination at 75 ? while maintaining a gain of 1 at the 75-? load. The switching time between any two channels is approximately 32 ns when both enable pins are driven. When designing a circuit board for this cable driver, care should be taken to minimize trace lengths at the inverting input. The ground plane should also be pulled away from RF and RG on both sides of the board to minimize stray capacitance. Current consumption of the cable driver is a modest 8mA.

Integrated AF power amps have seen great improvements in recent years offering improved power and easier use. The TDA1519C from Philips contains two power amplifiers providing 11 W per channel stereo or 22 W mono when the two channels are connected in a bridge con?guration. The special in-line SIL9P package outline allows the chip to be conveniently bolted to a suitable heatsink. The TDA1519CSP is the SMD version, in this case the heat sink is mounted over, and in contact with, the top surface of the chip.

11W Stereo Amplifier Circuit Diagram

The operating voltage of this device is from +6V to +17.5V. The two channels of the amplifier are different in that one channel, between pins 1 and 4, is a non-inverting amplifier, while the other between pins 9 and 6 is an inverting amplifier. It is therefore necessary in stereo operation, to wire the speakers so that one of them has its polarity reversed. Each amplifier has an input impedance of 60k? and a voltage gain of 40dB, i.e. 100 times. When both amplifier are used in a bridge con?guration, the inputs are in parallel so that the input impedance will be 30k?.

22W Stereo Amplifier Circuit Diagram

A combined mute/standby function is provided on pin 8. In its simplest form this can be connected to the positive rail via a switch. When the switch is open the amplifier will be in standby mode and current consumption is less than 100µA. When the switch is closed, the amplifier will be operational. A circuit is also shown that uses the mute input to prevent the annoying switch-on plop heard when power amps are ?rst switched on This is caused by the rush of current to charge capacitors C1 and C2.

Mute/Standby Switch Circuit Diagram

The circuit shown generates a ramp voltage, which is applied to pin 8. At switch on, as the voltage rises from 3.3 V to 6.4 V, the amplifier will switch out of standby mode and into mute mode allowing C1 and C2 to charge. Only when the ramp voltage on pin 8 reaches 8.5V will the amplifier switch into active mode. Protection built into the TDA1519C would seem to make it almost foolproof. The two outputs can be shorted to either of the supply rails and to each other. A thermal shutdown will prevent overloading and the power supply input is protected against accidental reversal of the supply leads up to 6V.

If you ever look at construction notes for building old detector type radios the type of headphones specified always have an impedance of 2 × 2000?. Nowadays the most commonly available headphones have an impedance of 2 × 32 ?, this relatively low value makes them unsuitable for such a design. However, with a bit of crafty transformation these headphones can be used in just such a design. To adapt them, you will need a transformer taken from a mains adapter unit, the type that has a switchable output voltage (3/4.5/6/9/12 V) without the rectifying diodes and capacitor. Using the different taps of this type of transformer it is possible to optimize the impedance match.

For the diode radio (any germanium diode is suitable in this design) the key to success is correct impedance matching so that none of the received signal energy is lost. The antenna coil on the 10 mm diameter by 100 mm long ferrite rod is made up of 60 turns with a tap point at every 10 turns; this is suitable for medium wave reception. If a long external aerial is used it should be connected to a lower tap point to reduce its damping effect on the circuit. You can experiment with all the available tapping points to ?nd the best reception. With such a simple radio design, the external aerial will have a big in?uence on its performance.

Tip:
If your house has metal guttering and rain water pipes, it will be possible to use these as an aerial, as long as they are not directly connected to earth. Those who live in the vicinity of a broadcast transmitter may be able to connect a loudspeaker directly to the output or if the volume is too low, why not try connecting the active speaker system from your PC?