Remote Volume Control ===================== By: Edwin van den Oosterkamp (eto@csa.nl). Appendices: Diagrams in IFF/ILBM "Diagram.IFF". Docs in english and dutch. Source code 8051 software "RVC.a51". Object 8051 software "RVC.obj". 8051 Hex file in Intel format "RVC.hex". VolumeControl executable for the Amiga. Preface ------- One of things that take the most of my time is using my Amiga. Music is for me a MUST. But the level of music is important, and varies with artist and song. When the volume is to low I will get frustrated that I can't hear the music at a decent level. When the volume is to loud I will not be able concentrate myself on the Amiga since the music will take my complete attention. And my stereo is at the other side of the room... So I wanted to operate the volume of my amplfier from my computer. Now there are multiple solutions for a "problem" like this: - I could buy an amplifier with remote control. But I like my amplifier and don't want to bay an other one just since I am to lazy to walk over and change the volume. - I could build a remotecontrol using servos on the volume knob. There is no room at all near the potentio meter of the volume, so it was a mechanical problem implementing this one. - Adjust the volume electronically. Yes! This is what became my solution: a small box containing some electronics connected between the pre-amp and the power-amp. The box used RS232 to be adjusted by my Amiga. The solution ------------ Crystal has a chip in its productline which fits exactly into my application. The chip can be seen as an PGA (Programmable Gain Amp). The IC (CS3310 to be more specific) is already stereo, so just one is needed. It is used in high-end applications so it will do at home also... The CS3310 is also equipped with a software-mute making sure that no sound is going through the device. Below there is a table giving some typical audio parameters of the CS3310 and see why it is used in high-end applications: Stepsize: 0.5 dB Minimal amp: -95.5 dB Maximal amp: 31.5 dB Error at 31.5 dB: +-0.05 dB Difference R and L: +-0.05 dB Distortion (2Vrms 1kHz): 0.001 dB Dynamic range: 116 dB Separation: 110 dB Output noise: 4.2 microVrms Offcourse the CS3310 is NOT equipped with a RS232 port. (The parallel port of the Amiga is capable of driving the CS3310, but that would not allow long cables between computer and VolumeControl). One way to convert a RS232 to a appropriate digital signal is using a microcontroller like the 80C31. The 80C31 is equipped with a RS232 port and multiple I/O ports. To obtain a speed of 9600Bd a clock crystal of 11.0592MHz is used. Since this is not the first application featuring a 80C31 with a 9600Bd serial port, this crystal is readly available (and not expensive!). This is also true for the microcontroller: it *is* a cheap device. RS232 utilizes voltages at approx 10V (positive and negative). These are not appropriate for direct microcontroller use. Therefore a RS232 line- driver is connected between the 80C51 and RS232. There exist a lot of these drivers and I selected the MAX232 made by Maxim, since it is a highly stable device. The MAX232 owns an internal (switching)power supply to convert the 5V supplied to the +10V/-10V needed for the RS232 interfacing. Back to the microcontroller. The software is loaded in a EPROM. It is possible to obtain an OTP (One Time Programmable) version of the 80C31 which is called the 80C51. But this one is more expensive and can be programmed just once. Also there is a version called the 87C51 which has an internal EPROM (including the erasor window) but for the price of that one it is possible to buy ten 80C31's... Using an EPROM with the 80C31 occupies some I/O ports, but since these ports are not used anyway, why not use an EPROM. The data and address bus of the 80C31 are multiplexed. To de-multiplex them a latch is needed (like the 74HCT573). Software -------- The software (source, object and hexfile) for the controller is included in this archive. If not please contact me. When the controller is put to power, it initializes the RS232 port for 9600Baud, 8 databits, 1 stop bit and no parity. To wake the CS3310 the controller shakes the /Mute signal a little. When all initializations are done, the controller transmits a simple "Usage:". This usage can be received by connecting a Amiga to the RS232 and using terminal software on the Amiga. With this terminal software the RVC can be sent commands. When the string is transmitted the CS3310 is set to a value of $c0 on both channels. This sets the amplification to 0dB. The instructionset used by the 80C31 looks much like the one of the z80. Compared to the instructions of the MC68000 there are a lot of small differences: Instead of "BSET.B #..." the 80C31 uses "SETB ..", but that is nothing compared to the MOV instruction: Comparing the MOV with the 68000 MOVE instruction we see that source and destination are changed! So, instead of "MOVE.B #0,Accu" the 80C31 uses MOVE A,#0... Power supply ------------ Except for the CS3310 all parts need just a 5V supply. The CS3310 needs a symmetrical 5V supply. Since I wanted to use a small adaptor for supply, the total inputvoltage must be kept low. But at the other hand: a component like the CS3310 must not be spoiled with a bad powersupply. Therefor I selected for the more expensive option by using a DC/DC converter for the supply. The NMH505S suits for this application: it is able to derive a +5V/5V supply from a single 5V input. An other problem with adapter supply is that those things are never decently stabilised. To stabilise the powersupply I added the 7805 and some capacitors. The 1N4001 diode is used as a kind of wrong connection protection. Around the CS3310 there are a lot of capacitors. These things are recommended in the application note by Crystal. This is also the fact for the 10Ohm resistor. These components should remove the noise on the analog lines made by the digital part of the CS3310. These components should be as close to the CS3310 as possible. The capacitor round the MAX232 are for the internal DC/DC converter of the MAX232. These capacitors do not need to be connected as close as possible, but the MAX232 and its surrounding components should be kept far from the CS3310 to prevent noise creation on the analog lines. Every IC must have its own 100nF capacitor over the supply! These are not drawn in the diagram. Amiga Software -------------- To enable the volumecontrol to be used with the Amiga, there is some software written for the Amiga also. it is useles to include the complete software here some basic routines are shown below: To transmit informtion, the serial post must be opened. Offcourse the SER: device in dos.library could be used, but I rather use serial.device since it better performance. Opening of the serial.device (KS2.0): OpenSer: MOVE.L 4.w,a6 ;a6 = Execbase. JSR CREATEMSGPORT(a6) ;Create a MsgPort. MOVE.L d0,SerMsg ;Store and test the MsgPort. BEQ.B Ser_Error ;result=0? No MsgPort! MOVE.L d0,a0 ;Place MsgPort in a0. MOVEQ #82,d0 ;ULONG Size IOReq-struct. JSR CREATEIOREQUEST(a6) ;Create IOReq struct. MOVE.L d0,SerReq ;Store and test the IOReq. BEQ.B Ser_Error ;Result=0? No IOReq! ;Make some default settings and open the device. MOVE.L SerReq(PC),a1 ;APTR StdIOReq. MOVE.L #9600,io_BAUD(a1) ;ULONG Baudrate. MOVE.B #$80,io_SerFlags(a1) ;UBYTE Flags: No protocol. LEA.L SerName(PC),a0 ;APTR Device name. MOVEQ #1,d0 ;Unit number. MOVEQ #0,d1 ;No flags. JSR OPENDEV(a6) ;Open it. TST.L d0 ;Test the result. BNE.B Ser_Busy ;Ne device? It is possible to set more default settings, Things which are not set here are used from the preferences. Everything opened must also be closed: CloseSer: MOVE.L 4.w,a6 ;a6 = Execbase. TST.L SerReq ;Test StdIOReq. BEQ.B Ser_NoReq ;No req? MOVE.L SerReq(PC),a1 ;APTR StdIOReq. JSR CLOSEDEV(a6) ;Gone is the device. MOVE.L SerReq(PC),a0 ;APTR StdIOReq. JSR DELETEIOREQUEST(a6) ;Gone is the IORequest. CLR.L SerReq ;Free the message port of the serial device. Ser_NoReq: TST.L SerMsg ;Test MsgPort. BEQ.B Ser_NoMsg ;No MsgPort? MOVE.L SerMsg(PC),a0 ;APTR MsgPort. JSR DELETEMSGPORT(a6) ;Gone is the Messageport. CLR.L SerMsg Ser_NoMsg: Both the open and close routines are written for KickStart2.0 and higher. Things like devicenames and variable storage should also be specified. When serial is opened (and before closing it) the serial may be used. using is not more than calling DOIO... ChangeVol: MOVE.L 4.w,a6 ;a6 = ExecBase. MOVE.L SerReq(PC),a1 ;APTR Serial-IOReq. MOVE.L #4,io_Length(a1) ;ULONG Size (4). MOVE.L #SerFile,io_Data(a1) ;APTR Buffer. MOVE.W #CMD_WRITE,io_Command(a1);Write command. JSR DOIO(a6) And this is how the string looks like: SerFile: DC.B $1b,'1',192,192 ;Instellen: 0 dB. The RVC "protocol" wants that the ($1b) is transmitted first. After that the "1" is transmitted and the bytes for left and right are transmitted. Looking back ------------ My prototype draws a current of 100mA. This current will be smaller when the controller uses the idle-mode to reduce power consumption. When using the prototype nothing of the digital switching signals was found on the analog terminals. When the CS3310 has no supply voltage, it has a rather low impedance, so the input signal is ruined. When making a switch to bypass the RVS both the inputs and outputs of the CS3310 should be disconnected from the audio. When there are any questions about this subject, don't hesitate to contact me.. Thank you for your attention... Edwin. Th. van den oosterkamp E-Mail: eto@csa.nl WWW: http://www.csa.nl/users/eto/index.htm