Redvix

As my DAC only have a single coaxial digital input I have a new need for a digital multiplexer / input selector.

These are the current requirements:

• Should allow for both Toslink optical inputs and Coaxial Digital inputs
• Expandable (possibility to add extra inputs as required to save initial costs and work)
• Should maintain signal integrity as much as possible
• Power should be supplied from a 9VAC output on the existing DAC
• Should introduce not ground loops
• Output should be coaxial digital
• Should display the current input (Would be nice but is not critical)
• Should display power status
• Should relay the status information from the existing DAC to the amplifier

Components:

• Stable power supply (9VAC to 5VDC)
• nput circuits for optical and coaxial inputs
• Multiplexer IC
• Interface for AMP controller interconnect
• Line Driver for Coaxial output
• 7SEG Display for Input status
• Display driver for the 7Seg Display

I have ordered some of the parts and I am planning and designing soon.

More information coming soon.

I have posted this for anyone suffering blotches, shadows, spots or discolouration on there Sony rear projector. I have performed a techie autopsy on my rear projection SONY TV in an attempt to see what exactly had happened. I have attached photos of various parts of the light engine showing the damaged parts for anyone interested.

About two years ago a friend gave me a broken Sony 50inch ear projection TV which I took it in the hope it could fix it. After a lot of investigation and despite the nature of the problem and the fact that the the errors indicated by the TV were totally false I tracked the problem down to a worn out bulb. I replaced the bulb for £150 and the TV worked perfectly. I was very happy to have gained a 50inch HDTV for the price of the bulb. After running perfectly for around one and a half years a strange blue blotch started a appearing in the center of the screen. The problem gradually got worse then for some reason started to improve until more blotches started to appear. The blotches were the obvious problem but the colour balance was all over the place and varied from point to point all over the screen.

After doing some research online I stumbled across this page as well as others:

http://sites.google.com/site/sonylcdrptvproblems/

This suggested that this problem was quite common on this TV and if fact Sony projectors in general. It is widely believed that the cause is down to insufficient cooling and ultraviolet filtration, causing optics in the light engine to degrade and fail over time.

Now I have a new TV I’ve made the decision to dismantle the light engine and see exactly what had went on inside to cause such a problem. As I had expected the optics had degraded exactly as described in every article I had read. In my light engine one of the colour filters closest to the light source was completely melted in the center. There was general discolouration on various lenses and filters but this was by far the most affected. I’m assuming this to be the cause of blue blotch in the center of the screen that over time had degraded to the point it became transparent again, almost correcting the original problem. This is proof enough for me that what is being said online about these projectors is accurate.

I personally think that a TV failing within the lifespan of only two bulbs is unacceptable. As I didn’t purchase the TV directly off Sony I am less concerned than others my have been but I won’t buy anything from Sony in the future.

I did notice that there was a large air filter on the light engine designed to filter dust from the cooling system. On my light engine the filter was VERY clogged. I’m sure this assisted with the degradation of the optics but if this was part of the problem then a user maintainable pre-filter would probably have been a better design choice than allowing a meltdown of the optics.

Here are some of the photos:

Since starting the control system for the amplifier there has always been a small but annoying problem with it. The amplifier has a protection IC onboard. One of its functions is to give the amplifier time to warm up. It will physically mute the output of the amplifier for a predefined time. The problem I have is that the startup time is not always constant.

Originally my software attempted to guess the delay time then indicated the full power on state after this time. This often caused confusion for people using the amp as the amplifier would indicate fully on yet no sound was produced.

To solve this problem I decided to build a simple interface allowing the controller to sense the actual state of the protection circuit. It is a very simple circuit consisting of a potential divider and opto-isolator. I build the circuit on strip board and connected it to the amp and controller.

After updating the firmware and testing I found a problem. The interface pulls the line low then the protection delay finally completes (When the output relay is closed). This causes problems when the amplifier first powers up. It takes time for the circuit to stabiles and the controller was sensing the end of the warm up period before the amp had fully powered up. I solved the problem by instructing the controller to wait some time for the amplifier to power up before checking for the signal.

This is now working as expected. When the controller indicates ON the amp will output sound.

I’d been waiting until I had the money and time before ordering the PCB and parts for the amplifiers input selector.

After just getting hold of new flat screen TV with the most pathetic sound possible, I decided to improvise a temporary input selector allowing me use of the amplifier with my TV as well as my Mac.

I built the selector using strip board and some relays that I originally purchased for this job around a year ago.

I drive the relays using a ULN2003A Darlington array and have used a set of phono sockets from an old Kenwood amplifier.

For now I still have enough pins left on the Arduino to make it work using one pin per input, this is not ideal and will not be the case in the final version.

I have not switched the input return lines / grounds so there is a possibility of ground loop occurring even though I’ve not had any problems yet.

I’ve also utilized the input selector to enable the mute function. To accomplish this I simply turn off all relays. This isn’t ideal as it leaves the input to the amplifier floating and lets some noise through. I will correct this in the final version.

I have been using the new input selector for about 3 weeks now and it’s working very well. It has not impacted on the sound noticeably if at all. I am happy at the result.

After making this change it became clear that I need to do some serious work on the amplifiers firmware to make it maintainable. Some of the most terrible code I’ve ever written is at the hart of this device.

So now I have a working hybrid gainclone amplifier with almost all the parts required to make it digital. My next problem after getting the DAC powered is to make the amplifier more flexible.

I need switchable digital and analog inputs for all my sources. I also want to add digital optical inputs as all of the devices I plan to use with the amplifier have only optical outputs.

My plan is to create two new PCB’s. The first to switch the analogue inputs to the amplifier. This will accept four analog inputs. One of these analog inputs will be for the DAC and will be an internal connection. It will be relay based as I set down in my initial plan and will be controlled via a serial data from the controller. It will be expandable so more boards can be added if more inputs needed.

The second board will be for digital source selection to the DAC. It will have three optical and three coaxial inputs. It will serve two functions. The first, to convert three optical inputs to coaxial and the second to route the required input to the DAC’s input. The serial data from the controller will be passed from the analog input selector to the digital selector saving I/O on the controller.

The digital board will accept an 8bit command from the controller and using three DPDT relays will route the requested digital input to the DAC.

When selecting an input I wanted the controller to first power-up or power-down the DAC as well as the digital input selector based on the input type. This should save power and reduce heat in the enclosure. It will then output 16bits of serial data to the analog input selector which will use the first 8bits to select the analogue input then send the remaining 8bits to the digital input selector.

I received the DAC kit. It was bought from eBay under the name “CS8416+AK4393+5532 24BIT 192K 2496 DAC Kit”. It was available from few different sellers but I went for one in the UK.

Here are some of the specifications:

• CS8416 Digital Audio Receiver
• AK4393 24bit 192K DAC Chip
• 5532 Op-Amp
• Power Supply: 15V – 0 – 15V + 0-9V (Advertised as 13-15V x2 + 9-15V or 13-15V x2 only)

The quality is good. The PCB is very well made and the parts are all of good quality. The first thing I noticed about the kit is that all the smaller surface mount parts: three voltage regulators, the AK4393 – DAC chip, a Hex Inverter and the CS8416 – Digital Audio Receiver were already mounded to the PCB. This was a big help as I was not looking forward to soldering these parts with the tools I have available.

There was no documentation with the kit I received. Only the silkscreen on the PCB it’s self. This was enough for me to assemble the board but I still had some questions regarding the power-supply etc.

There was no obvious indication as to how to wire up the power supply’s. I assumed that there was it was (15v) (0v 15v) (0v) from right to left on the the connector. To make sure, I hunted down and eventually found myself the circuit diagram for this board. It turns out that I was correct about the power supply but I had wanted to be sure.

Once I completed the assembly I powered it up using the transformers I had in the gainclone amplifier. For the 9Vac supply I used one of the 0-9v secondaries from the valve heater transformer. For the 15-0-15 I had to get creative. I didn’t want to wait for the custom power supply before testing the DAC so I bypassed the digital controller in amplifier so power was always on the the amp and used the transformer from the auxiliary power supply (normal used for the controller) to power the DAC instead. Loosing all digital control’s while still having an amplifier to test the DAC with.

I connected the power supply to the DAC and tested using the only non optical source I had available, the digital output of my file server’s DVD drive.

The power light came on but no sound. I experimented again and again and nothing. I eventual came to conclusion that there was a serious problem with the DAC. Interestingly there was no “ERROR” or “NO AUDIO” indication displayed. I would have expected at least for the “NO AUDIO” LED to come on when unplugging the digital source but there was nothing.

I started looking over the circuit diagram I found online. The LED’s are driven by a hex inverter connected to the CS8416 chip and the hex inverter was getting power.

Upon further investigating it turned out that there was a very low voltage on the analogue power pins of the CS8416. I traced this back to a really big mistake made during the build. I had connected the two voltage regulators the wrong way round. I put the positive and negative regulators in the wrong locations on the PCB.

After fixing this problem I tested this again and it worked at last. Hopefully I have not damaged any parts of the DAC. It doesn’t look like I have but you never know.

Overheat

I ran the DAC for a while and was very impressed with the sound quality. However I noticed the two regulators getting VERY hot. I shut down the amp and decided to attach a small heat sink on them.

Again I tested and ran the DAC for a while. The heat sink was doing its job well and the regulators were quite cool now. Until POP!! then no more sound. Actually there was some sound just very very quiet. I instantly switched off. I checked everything and noticed that is smelled hot and it wasn’t the regulators.

I started touching the parts one by one until I finally burnt myself quite badly (6mm blister on my finger badly) on one of the AC-DC rectifiers. I started investigating again, measuring everything.

The 15Vac transformer that I have been using for months with the auxiliary power supply turns out to be outputting 18Vac. This would explain the regulators getting hot in the first place.

After waiting some time I reconnected and tried again and it worked. I’m not sure what happened. I’m guessing a safety feature a component may have shutdown and protected the circuit but to be honest I don’t really know or care because whatever it was must have been temporary.

I’m unsure why the rectifier got so hot but I’m going to assume for now it was because of the higher voltage supply. I’m not going to use the DAC again until I get a suitable power supply. But I am convinced it’s working and is suitable for the amplifier.

Introduction

This article is a guide to repairing the Apple Wireless Mighty Mouse scroll function. It may be useful if your mighty mouse is not scrolling down, up or in any direction. If you have tried everything else and nothing has worked then this should work.

Before resorting to this technique you should try some of the other methods around to repair the sticking mighty mouse scroll ball. The method I find most effective is to turn the mouse upside down and rub the ball with a clean damp cloth. This usually works well but sometimes nothing will fix and the only thing left to do it strip it down and clean things properly.

This guide has been written for the wireless mighty mouse but it can be adapted for the wired version even though it is a slightly more difficult to dismantle (I’m sure the cable is glued in one place).

Disclaimer

The Apple Mighty Mouse is not designed to come apart. This technique does involve dismantling the mouse. If you are trying this method it should only be because nothing else has worked and this is a last resort. Doing this will obviously void your warranty and I take no responsibility for any damage done to any property or to you as a result this guide.

Removing the Bezel

The first and probably one of the most difficult things to do successfully is to remove the plastic ring on the bottom of the mouse. The reason being that apple glued it on. Not clips, not screws, not friction but glue WHY? Anyway I found the best way to tackle this is to use a very thin long and sharp blade to gently break the glued joints. I used a cook’s knife. It spreads the load well and does not chip the plastic easily. This is quite dangerous so be careful, I’ve slipped a couple of times. Thankfully it is not glued around the entire surface and only at specific points so it breaks away cleanly at these points. I would not advise puling up on the ring as it will probably snap or at least bend. The thickness of the blade should be enough to crack the glue. Work your way around until the entire bezel is free.

Open the Mouse

To open the mighty mouse you must first locate the two retaining clips at the front of the device. Use something small and pointy to gently release both from the body of the mouse while gently pulling the base down. Once the front clips are free the base should now hinge at the rear. Now unclip this hinge also.

Warning (be VERY careful when removing the base. It contains all the batteries and it’s heavy. If you let it fall it will probably tear the ribbon cables connecting the scroll ball assembly and the buttons sensors.)

Locate and Remove Trackball Assembly

It is possible to open the mouse enough to access the trackball assembly on the top of the body. Remove the three screws and unplug the connector. To do this you must unlock the socket by gently sliding out the dark clips on the side of the connector in the director you would remove the cable. The clip will move about 1mm and will release the cable from the socket.

Opening the Trackball Assembly

Now that you have the trackball assembly on its own you have to open it. The ball is held into the assembly by a white plastic retaining cover. You should be able to see the main clip in the picture. You need a sharp pointy tool like a scalpel or pointy blade to release it from the bottom.

When releasing this clip, carefully remove the retaining cover without breaking the other three smaller clips around the block. This device contains many small parts that can be easily lost. Remove the ball and the four rollers for cleaning.

Cleaning

The chances are that the trackball assembly will be incredibly dirty and full of fluff and other nasty stuff. All parts should be cleaned as carefully as possible. You should clean all of the following parts:

• The ball it’s self
• The ball retaining cover
• All four rollers
• The hole in mouse body
• The remainder of the trackball housing

I used 60/40 isopropyl alcohol and water (DIY rubbing alcohol) you should probably use lint free tissues/cotton buds but I don’t have any. It doesn’t have to be dust free as it will get dirty again but the cleaner the better.

Reassembling the Trackball

This is a bit tricky but you just have to be careful. You must first place the rollers back where they belong. If they flew out when you dismantled it just have a look at the picture. Be careful to position them so the slots or groves on the shaft rest on the little mountings in the housing. They are magnetic and may “want” to go into there correct positions.

Place the ball back in the center and replace the retaining cover. The cover will only fit on one way, with the large clip at the front just as it was removed. Don’t force it. If it doesn’t want to go back on then re-check the position of the rollers.

Reassembling the Mouse

I found the easiest way to do this was to start by connect the trackballs ribbon cable to the board. Insert the cable into the socket and lock in back in place with the clip you released when removing it. It should be possible to reinsert the three screws and reattach the trackball to the mouse body with the cables still in place. You could do it the other way around but I found that more difficult.

Reassemble the mouse by clipping in the rear hinge then closing the base until the front two clips engage.

Test the mouse. It should be working like new. If you’re happy with it, carefully glue the plastic bezel back on the bottom. I used superglue and as long as you are careful not to get it on the shiny white apple plastic you will be ok. Re-glue it in the same way it was glued originally gluing the same points around the bezel. This should allow it to come apart again just as easily in the future.

Conclusion

Hopefully this guide has helped some people out. I believe the apple wireless mighty mouse is worth fixing. IMHO it’s a comfortable mouse and the scroll ball / trackball is very useful. This repair is a bit fiddly but can be done fairly easily. Any comments are welcome.

I have finally bought a strobe light, well a kit from eBay. I’ve wanted a strobe since I was a kid. I have no idea why but I just love them. You can buy strobes ready build for a reasonable price but I found this kit on eBay and though I get it for a bit of fun.

Building this simple strobe from a kit may help me better understand how these circuits function allowing me to move on to something a bit more impressive.

Warning

Strobes, even these small ones utilize high voltages (sometimes VERY high) if working with a circuit of this type be very cautious. Even when not connected to a power source the capacitors can hold enough charge to mess you up. Just bare this in mind when playing with this type of circuit.

It’s also worth mentioning that it’s possible for strobes to trigger seizures in people with photosensitive epilepsy so you should be carefully firing one of these things around people although the risk is lower when using a relatively low frequency strobe like this one.

The kit

This circuit is specified with a maximum adjustable frequency of 10Hz meaning at it maximum speed it will trigger ten times per second. This is a fast for a cheep strobe and good enough for my first strobe. It’s harder to make a strobe flash faster and therefore faster strobes are more expensive.

It’s not the best quality kit I have bought but I didn’t pay much for it. The kit came with very bad instructions but it’s very simple and there was at least enough information to work out where the components go. The PCB has mounting holes but no solder mask and has a very cheep silk screen. The lack of onboard fuse was a bit worrying and there is no switch. This could easily be added into the enclosure but an onboard fuse would have been nice.

The kit uses a small ‘U’ shaped xenon bulb and is powered off mains power (230v in the UK). It comes with two pots, one of which is fitted to the PCB. One has a shaft for adjustment and the other is adjustable with a screwdriver only. For what I could make out in the instructions the shiftless pot is used when a separate enclosure is purchased with the kit. I fitted the pot with the shaft for easy adjustment as I plan to make my own enclosure.

I assembled the strobe in around ten minutes and was anxious to test it. I probably (definitely) should have connected a 1A fuse in series with the circuit to protect against any problems but I didn’t. On this first test it functioned as expected with the only problem being that the frequency appears too be far from the specified 10Hz max. I may measure this some day but I’m happy enough that it works. I did notice during testing that the circuit did produce a lot of heat. This was not just the bulb as you may expect but most components on the board get quite hot. I wouldn’t like to run this for any prolonged time but you really shouldn’t anyway.

Conclusion

The kit worked as expected. The PCB was of low quality but I could tell that in the picture before I purchased it and it does its job. The strobe bulb produces a good bright flash and is fast enough to be used for in for a party etc. The instructions were not good but contain just enough information for someone to successfully build the kit. I think with the modification of a decent enclosure, fuse and switch it would make a useful strobe. Was definitely a fun build and am glad I purchased it. I will still have to build an enclosure to make it useful and might look into speeding it up but that’s for another post.

Now I would quite like to build a more powerful strobe from scratch.

The arduino is my favorite microcontroller development platform. It consists of a collection of open-source boards based around the Atmel AVR microcontroller chips, a development environment based on processing, and a language similar to C++ used to program the microcontroller.

It can be used by hobbyists and professionals alike. In genera it’s a good introduction to microcontrollers. The hardware can be easy adapted for use in a professional project.

The arduino comes in many forms but thay are all based around the Atmel AVR chips. Most contain all the basic components required to power, program and interface the chip with other devices.

At this time the most common version of the Arduino is the Arduino Duemilanove. This board along with a few of the others possesses a standardised set of female header sockets that allow the device to be connected not only by wires to a breadboards, external devices and also to a wide collection of PCBs known as shields. These boards are designed to work with the Arduino family are usually plug-in modules that perform a particular functions. For example there are shields that contain temperature sensors, LCD screens, accelerometers, pressure sensors, motor controllers and many other devices. You also get shields for prototyping. These are basicaly just breadboards or proto boards that can plug directly into the Arduino standard headers.

My preference is to use the Arduino Nano in most of my projects. The board contains almost everything contained in the Arduino Duemilanove only it is the size of a large chip. It still has its own USB port and a build in LED on pin 13 however it does not have the standard header pins.

I like this variant mainly because of it’s small size, it’s relatively low power requirements and it’s ease of use. I will not go into great detail on the arduino boards as there is already a mass of information available. If you want to find out more you can start by visiting http://arduino.cc/en.

If you are at all interested in learning about microcontrollers I would seriously recommend getting one of these to experiment with. They are cheep and most versions have a built in USB to serial chip and a USB socket. All you need to do is download the Arduino software which happens to be available for MAC, LINUX and Windows, plug the computer into the device and your set.

I will be posting some programs for the arduino when posting updates on my current projects so you can check them out if you want to get an idea what I use them for and how simple they are to program.

I have been waiting some time to find a DAC kit of reasonable quality and price on eBay.  Currently my amplifier has only a single analogue stereo input.  My plan has always been to have multiple analogue and digital inputs.

With space inside the enclosure being  limited I have not had the ability to add these new features.  The main reason for the lack of space is the ridiculous amount of transformers required to provide the various voltages required by the amplifier preamp and controller.  Once I settle on a specific DAC and then redesign the auxiliary power supply I can have a new transformer custom made to replace all the others. This will free up enough room inside the enclosure for the DAC it’s self and the other components I wish to add.

I finaly found this DAC kit on Ebay.  Its power supply demands are quite simple. The size of the pcb is acceptable to me and the quality looks to be quite good.

The truth is that while I do understand what the DAC does and what is consists of im not an expert on what DAC chips, op-amps and power supplys are the best.  I have done some research on some of the components in this kit and it does appear that many of the chips used are also used in some very high end external sound cards etc. It looks like the board is more than good enough for what I’m looking for. I just want a DAC that is going to be an improvement of the built in DAC in my MAC, PC or TV and I feel this is the one I’m looking for.

This has now been ordered without a power supply. I plan to build it and test it with what I have. I will also need an optical to coaxial converter as I only have an optical digital output on the Mac.  I will post the progress of the build under the category HiFi DAC Kit.