User Guide - Electronics DIY
Contents
1. tube amplifier transformer Schottky type diodes are applied in stead of basic rectifier diodes since schottky diodes do not generate recovery spikes To further eliminate such effects a 4 0nF capacitor was added to filter the AC voltage Clearly the schottky diodes and low drop regulator together enable operation from the low 6Vac 2 Rotary switch Connecting a rotary switch for manual volume control and channel selection is optional the circuit can be used fine from a IR remote only The applied type of switch is a rotary pulse generator which can be turned around and around without mechanical blocking It uses 3 connections one common pin connected to ground and 2 signal pins denoted Vol a and Vol b in the schematics The microcontroller has a weak pull up on these two signals So if the switch is not connected you should measure 5V on these The switch will in steady state leave either both pins open at 5V or short both to GND OV When the switch is in transition one of the pins will precede the other in its transition The rotation direction is derived from this transition order Currently use a print mount version of this switch alternatively a front mounted version is also available The front mount version does not fit my PCB needing a few wires between its contacts and the PCB but it does have an M7 wire and screw for front plate mounting Note that these switches also have a built in push button functio2. AZ ele alee oem esie vem 00 90m 9007 AON YOTS 49 OYeNUS 4 PeyrIIMS Y ueAcoupu f tHe oeoo o Sizes are in millimeters Screw holes are 3 2mm diameter they are centered on a 50 mil raster The height of the components above the relay resistor print is typically 22 mm If you really must push this you can reduce this height to about 11 mm The height of the components above the display PCB surface is mm which is the height of the 7 segment displays itself Happy listening Jos van Eijndhoven March 2007 11
3. User Guide For the IR remote controlled audio volume and channel input selector This document describes the dual microcontroller design as of November 2006 See also the corresponding website at hittp jos vaneijndhoven net switchr design html R41 R G lt AL 4 al hes it ia T 900Z unf uotsa n AOLENUSIIY PSYDIINS YI Q u aoypuf 17 uea sor O q R21 R22 R23 R24 R25 R26 R27 RZ 8 R29 R30 R31 R32 Document version March 19 2007 Characteristics The described attenuator provides infra red remote control for audio volume and input channel selection Both volume and channel selection is performed through miniature relays Six tiny relays implement a stereo 64 step logarithmic attenuator The combination of relays with high quality small signal contacts and prime quality resistors provides a top class audio volume control audibly better then conventional potentiometers that employ a sliding contact over a resistive layer The chosen sealed relays will maintain their contact quality over an extremely large time span A standard setup employs a small front control PCB for IR reception a visual display feedback and an optional manual switch control and one relay PCB that performs the actual audio handling This relay PCB provides relays for a 2 channel stereo volume control and input channel selection Multiple of these PCBs can be tied to a single front control module 2 prints can be used for ba
4. dditional relays can be controlled through the aux signals indicated on the schematics and on the PCB The power down button causes the PGC signal pin 5 of the 5 pin connector to value 0 In power down mode the attenuator does not react on volume up down or mute commands The power down mode is left PGC gets raised upon a channel select command P9 is not meant to get attenuator reaction upon an extra button but merely changes the attenuator mode of display operation In its default mode the attenuator shows on its display a reaction on the last command by showing the newly selected input channel or the newly selected volume level for about a second After a second the display will return idle black again If the P9 location is programmed with the same key as power down then the attenuator display will show channel selections for a second but then keep showing the audio volume level Only in power down mode it will make its display idle black Ready to use Waiting a few seconds or pressing a recognised command code will exit the program mode and enter normal use mode Sending a command will cause the resulting new volume or input channel to be shown on the display for a few seconds After that the display will revert to its default or if P9 was programmed the volume setting will be retained Volume levels range from OO to 64 Input channels range from 1 to 4 or if programmed thr
5. h as menu OK or FastForward Assume for this text that this button is OK The selector reacts with PZ on its display b You can freely press OK repeatedly thereby cycling through P1 P2 P9 P1 If you do not press anything for about 5 seconds the display will go back to _ indicating that you left configuration mode c If the display shows P1 and you press any button other than OK that button code is stored in non volatile memory and will be used later for Volume Up The display reacts with 1 to confirm the coding of function 1 Pressing OK again will move you to a next button to configure With repeating steps b and c and or a you can configure the following button codes Pl Volume Up P2 Volume Down P3 Mute on off P4 Input channel Up P5 Input channel Down P6 Input channel select numeric 1 P7 Input channel select numeric 4 maximum channel number P8 Power down PQ Display mode The numeric keypad on your remote can be used to select the audio input channel For this purpose the signals of the first button 1 and the last button 4 are to be programmed As exception you could program a different number of input channels by choosing another value then 4 A maximum up to 7 can be used by connecting extra relays outside the provided PCB three a
6. in its white annotation text the resistor names numbers are not appropriate The resistor values must be mounted in the same left to right order as in above table which is also the left to right order in the schematics The Vishay Beyschlag resistors that provide for the 100K or 22K attenuator have a 5 ring color code with a final brown ring for their 1 tolerance The color coding is documented for instance on http www logwell com tech components 1resistor_color_code html or with a calculator on http www samengstrom com nxl 10116 5_band_resistor_color_code_page en html Building the attenuator Most of the PCB assembly process hardly needs explanation the schematics has clear component types and identifiers These identifiers are also annotated on the PCB Some remarks are probably helpful for the connections towards components outside of the pcb 1 Power supply AC power should be applied to the small 2 pin connector The circuit will operate from a 6 0 to 7 5 Vac transformer A pair of a display and a relay PCB together take a maximum current of 250mA A relay PCB alone takes a maximum of 185mA You can check that the DC voltage on C1 is between 6 5Vdc and 10Vdc Higher voltages might cause the LM2940 to get warm typically use a rather small clip on heatsink If you connect the attenuator to a 6 3Vac of your tube amplifier transformer you will like to avoid any risc that this rectifier back fires dirty effects into your precious
7. k input 22k output attenuator The other rows shows values for a 47k input 10k output and a 22k input 4 7k output attenuator The attenuations are chosen such that a good match is obtained with resistor values from the basic E12 series of values The Dale RN6OD resistor set that recently tried uses values from the E96 series In the table annotated beneath their value the number that is printed on these resistors followed by a letter F R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R31 R32 R41 R42 R43 R44 R45 R46 R47 R48 R49 R50 R51 R52 R51 R52 100K 56k 33k 150k 27k 15k 56k 56k 100k 2 7k 180k 100k 1 8k 1 2M 22k E12 47K 27k 15k 68k 12k 6 8k 27k 2 7k 47k 1 2k 82k 56k 1k 560k 10k E12 ATK 27 4k 14 7k 68 1k 12 1k 6 81k 27 4k 2 74k 47 5k 1 24k 82k 56 2k 1 0k 562k 10k Dale 2742 1472 6812 1212 6811 2742 2741 4752 1241 8202 5622 1001 5623 1002 22K 12k 6 8k 27k 4 7k 2 7k 10k 1 2k 18k 560 39k 22k 390 270k 4 7k E12 In some sets an alternative value of 11 8k is used denoted with 1182 would advise to mount the Dale resistors with their value identification visible upwards so that you can easily check later that they are all mounted in the proper position This picture is an example of my own test version showing the mounting positions with readable values Please note why included this photo that this version of the PCB has an error
8. lanced symmetrical audio systems 3 prints for 5 1 surround systems or 4 prints for 7 1 systems Traditional potentiometer usage provides a constant input resistance and variable output resistance The switched attenuator in this design in principle works the other way around it has variable input resistance and constant output resistance However due a specific design trick the default attenuator resistor values provides a lower output resistance for the lower half of the volume steps You could use this attenuator as a complete passive pre amplifier It depends upon your power amplifier whether the relatively high output resistance is OK for your system In general tube amplifiers feature a high input resistance and might do fine Otherwise you can actively buffer the output signal of the attenuator and or create your own integrated amplifier with this PCB In general would hesitate a little to drive inter chassis audio cables from just this passive attenuator The device has volume levels from 00 up to and including 64 Volume levels 01 to 64 span a dynamic range of 69dB with 63 steps of 1 1 dB Volume level 00 really disables the input signals giving zero output The default resistor set that apply is a series of 12 resistors per channel R21 R32 and R41 R52 with values of 56K 33K 150K 27K 15K 56K 5K6 100K 2K7 180K 100K 1K8 Normally this would provide a suitable replacement for a 100K potentiometer With these va
9. lock amplifiers where you might choose to keep LGND and RGND separated Some of you might also prefer not to use wire bridges but couple the grounds through small resistors e g 100Q Multi channel set up The design does support symmetric balanced audio or multi channel 5 1 or 7 1 surround audio The extra audio channels are handled by connecting extra relay boards to the same front display board Multiple relay boards connect to one display board in the following way Each relay board connects to the 6V 7 5V AC power The new PCBs of Nov 06 provide an AC out pair of pins for daisy chain wiring One relay board connects with at least the 3 center pins of the 5 pin connector to the display board Connecting the left most and right most pins is optional but has no function These pins are primarily added for programming the PIC micro controller All relay boards connect their GND and PGD located at pins 3 and 4 of the 5 pin connector The new PCBs provide 2 extra output pins for these signals for daisy chain wiring The drawing below shows this set up for a 2 board symmetric audio configuration in in2 in3 in4 out in1 in2 in3 in4 out ES 5 GND To optional power relay If you want to mount two relais boards closely above each other you might want to mount the capacitor C1 lying flat on the PCB instead of standing upright Accordingly you can bend the LM2940 horizontally
10. lues the input output resistance levels and attenuation as function of the volume step number are as shown in the figures below Impedance Attenuation 200000 Chart Are a 1 6 11 16 21 2 31 36 41 46 51 56 61 0 00 150000 10 00 ene Si oe 50 00 50000 aaa E 7 9 re o SE EEEE ete soe cute sever woce revere 80 00 1 6 11 16 21 26 31 36 41 46 51 56 61 With these resistor values the output resistance changes from 22K to 1K8 at the 32 nd step The curves show the behavior when the attenuator is loaded with an external amplifier resistance of 100K Unfortunately the drop in output resistance makes the attenuation of the 32 nd step dependent on this load resistance An alternative configuration would keep the output resistance constant at 22K all over and have all attenuation steps independent on the load resistance That would be obtained by changing the final two resistor values of the chain 100K and 1K8 into 1M2 and 22K Dropping the output resistance for the lower volume settings was chosen to potentially reduce hum pickup for the low play levels Note that the combination of the 22K output resistance and the 100K load resistance leads to a minimum attenuation maximum signal level of 1 7dB A OdB pass through would only be obtained for an infinitely high load resistance The table below provides an overview of potential resistor values to create the attenuator The first row of values is used in the schematic drawings for the 100
11. n by pressing their shaft Therefor a separate channel select button as described in the following paragraph is not required Print mount version of the rotary switch default Front mount version of the rotary switch upon request Channel select button For manual channel input selection a push button can be optionally connected between the 2 pins marked with push button on the display PCB Every press and release will move to the next input channel with wrap around at 4 by default Power switch output The relays PCB allows to optionally connect a power switch relay to switch on off other equipment from your IR remote Obviously this function only works if the power of the attenuator itself remains on Power switching is triggered by a dedicated button on your remote control or by keeping the rotary switch pressed down for about 2 seconds When switched to the off state pin 5 on the programming header PGC will be OV otherwise it will be 5V active high Note that you cannot directly connect a heavy power relay between this PGC pin and the digital ground pin 3 on this connector due to the 5V and 25mA current limitation of the microcontroller The Omron G6K seems the ONLY 5V relay with at least 200 ohm coil resistance Power relay Opto coupler or l solid state relay Small signal 1K relay G6K 150 PGC PGC PGC L Some circuit options to drive an external power switch relay C
12. nd and then reverts back to showing just The small dot is merely a power on indicator The P indicates that the device is in a mode susceptible to programming The J indicates that audio input channel 1 is currently selected When sending a IR signal to the device three reactions are possible e This indicates that the device cannot handle the format of the received IR signal You have to find yourself a different remote or for a multi brand remote experiment with a different mode This error signal is only displayed during the short power up programming mode e 3 Some one or two digit numeric result means that the device performs a proper reaction on an understood button e No reaction whatsoever This indicates that the device doesn t know what to do with the received IR signal Your remote might be compatible but the volume controller has no action associated with this particular button code This would be the expected result for a new still unconfigured attenuator Configuring your attenuator With a compatible IR remote you can proceed with learning your attenuator to react properly on your favourite buttons You again power up the device obtaining P on its display which indicates susceptibility for programming a Within these 5 seconds or so after power up you press some button on your remote that you do NOT want to configure in the selector and was NOT configured earlier suc
13. onnecting the display PCB with the relay PCB s The display PCB must be connected to the relay PCB Each PCB has a 5 pin connector and normally will provide a connector set for this Connecting a pair of PCBs through these 5 wires works fine The 5 pin connection is also used by me to download the firmware into the PIC microcontrollers For normal operation however only the middle three pins are actually needed For symmetric balanced audio or multi channel audio set ups see the description in the next section Grounding The PCB duo implements three electronic circuit sections that are electrically totally isolated from each other a The digital control circuit with the microcontrollers the power supply the display and the relay coils b left audio resistors and relay contacts c right audio resistors and relay contacts Each of these three circuits has its own ground respectively GND LGND RGND Because the PCB doesn t tie these together you can still choose apply your own grounding policy as to whether and where to connect these grounds However a totally unconnected digital ground seems to induce hum and interference in the audio part of the attenuator For typical usage would recommend to tie together all your ground signals power and signal The new Nov 06 version of the PCB supports this by soldering two small wires in the locations R1 and R2 Maybe there are a few special cases such as with totally separated monob
14. ough P7 a different upper limit Channel select up down has cyclic wrap around The mute command both mutes and unmutes volume changes also unmute The power down command does not also symmetrically power up mainly because holding such a key pressed on a remote would cause undesirably quick power on off cycles The power up is automatically induced by input channel selection The attenuator display PCB stores its last used volume and channel selection in non volatile EPROM memory At its next power up it reads those settings to start up in its previous state One last warning For its audio signals the attenuator is truly passive Its maximum output resistance is not higher then that of a normal potentiometer but it retains its high resistance across a much wider volume range Some power amplifiers do not like to be driven by such resistance or in some system set ups extra humming might be picked up Please verify in your own system that an output resistance of about 10Kohm for my default 47K Dale resistor choice does not cause you any problems If 10K is problematic the attenuator needs to be followed by a driver stage to lower its output resistance For which am developing a rather nice option Of course choosing other resistor values can also give you a lower output resistance at the cost of a lowered attenuator input resistance 10 Layout and sizes 23 50 13 97 irae a Tene eS leno Se po RE A
15. pointing outside In special applications it might be nice to operate the attenuator relay PCBs further away from the display PCB in particular integrating a relay PCB inside each monoblock amplifier In that situation only the data signal pin 4 and the digital GND pin 3 needs to be distributed and the display PCB can take its 5V supply from a local source It is for such a configuration that each relay PCB has its own power down output signal A series resistor of 2200hm is recommended in the data signal between the display PCB and off case connectors to improve safety and damping Remote controller compatibility First thing to do is find your own remote control handheld that transmits IR signals in a format that is understood by the device In practice there exist many different formats some of which are shared by multiple companies brands Clearly within each format many different codes are used related with activating different functions on different devices As of yet my volume controller understands the widely used Philips RC5 and RC6 formats All generic multi brand IR remotes can send these formats Personally am using an old hauppage remote The formats used in modern Sony remotes are not yet supported they might be in a future version of the firmware If you power up the attenuator the display PCB and everything works correctly the display shows P for about 5 seconds then show J for about 1 seco
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