An Oscilloscope Calibrator. --------------------------- Technical Specifications:- -------------------------- Calibrated Frequencies........ 100Hz, 1KHz (and 10KHz, see below). Calibrated Output Voltages.... 1V, 100mV and 10mV, (manually switched). Software Attenuation.......... 0dB and -20dB. Output Impedance.............. 10 KilOhms. Frequency Accuracy............ Better than + or - 1%. Amplitude Accuracy............ Better than + or - 5%. Frequency Wave Shape.......... Square Wave, 1:1 Mark/Space Ratio. Frequency Rise Time........... Better than 10uS. Unwanted Hum and Noise........ -30dB below fundamental signal. Note:- ------ The specifications above apply only to a Standard A1200 and may NOT be the same for an A500(+) A600 etc. etc. ---------------------------------------------------------------------------- Overview:- ---------- This tool is used to set up Oscilloscope Time Bases, Vertical Deflection Amplifiers. Synchronisation and trigger settings can be checked also. Note:- This is the first project with full construction information. As this is used to calibrate a serious piece of test equipment, it has to be made as well as possible so that the specifications remain the same for anyone who builds it. ============================================================================ Construction of the Oscilloscope Calibrator. -------------------------------------------- Part 1:- -------- A):- ---- Construction of the Output Cable:- ---------------------------------- 1) Remove the outer sleeving on one end of the RG58 Coaxial Cable approximately 30mm long. 2) Fold back the braiding over the sleeving of the cable. 3) Trim the braiding to about 8mm long. 4) Strip approximately 20mm of the insulation off of the inner conductor. 5) Tin the inner conductor. 6) Screw on the PL259 plug, feeding the inner conductor down the centre of the plug. 7) Solder the inner conductor to the PL259 centre pin. 8) Trim off any excess braiding and solder from around the PL259 plug. 9) Measure the length of the Coaxial Cable to approximately 1000mm from the tip of the PL259 plug and cut to this length. 10) See the ~Cables.drawing~ and the ~Extras.drawing~. 11) Dismantle the BNC plug. 12) Feed the Nut, Washer and Rubber ~O~ Ring down the opposite end of the RG58 Coaxial Cable. 13) Remove the outer sleeving on the opposite end of the RG58 Coaxial Cable approximately 8mm long. 14) Fold back the braiding over the sleeving of the cable. 15) Trim the braiding to about 3mm long. 16) Strip approximately 3mm of the insulation off of the inner conductor. 17) Tin the inner conductor. 18) Place the Pin over the tinned inner conductor and solder together. 19) Feed the Bush over the Pin assembly so that it is in contact with the Braiding. 20) Carefully place the Body of the plug over the whole, ensuring that the Pin goes through the hole provided in the plug. 21) Screw together and tighten up. 22) See the ~Cables.drawing~ and the ~Extras.drawing~. 23) You are now ready to go on to part B). B):- ---- Construction of the Input Cable:- --------------------------------- 1) Remove the outer sleeving on one end of the Audio Coaxial Cable approximately 20mm long. 2) Part the braiding from the inner conductor. 3) Place a piece of Heat Shrink Sleeving over the Audio Coaxial Cable. 4) Using the soldering iron shrink the sleeving over the ~Y~ joint to give approximately 15mm of braiding and inner conductor left. 5) Strip approximately 2mm of the insulation off of the inner conductor. 6) Tin the inner conductor and about 3mm of the braiding also. 7) Measure the length of the Coaxial Cable to about 515mm from the tip of the inner conductor and cut to this length. 8) See the ~Cables.drawing~ and the ~Extras.drawing~. 9) Dismantle the PHONO/RCA plug. 10) Place the Body of the plug over the opposite end of the Audio Coaxial Cable. 11) Remove the outer sleeving of the opposite end of the Audio Coaxial Cable approximately 10mm long. 12) Part the braiding from the inner conductor. 13) Strip about 4mm of insulation off of the inner conductor. 14) Tin the inner conductor and about 5mm of the braiding also. 15) Connect the inner conductor to the inner tag of the PHONO/RCA plug. 16) Connect the braiding to the outer tag/clamp of the PHONO/RCA plug. 17) Trim off any excess wire or solder as required. 18) Screw the Body of the PHONO/RCA plug to the soldered assembly. 19) See the ~Cables.drawing~ and the ~Extras.drawing~. 20) You are now ready to go to ~Part 2:-~. ---------------------------------------------------------------------------- Part 2:- -------- The Drilling Details:- ---------------------- 1) Dismantle the Die Cast Box and save the top and the screws. 2) Using the correct diameter drills, mark out and drill all of the holes as per the ~Drilling.drawing~. 3) Deburr all of the holes. 4) You are now ready to go to ~Part 3:-~. ---------------------------------------------------------------------------- Part 3:- -------- The Mechanical Assembly:- ------------------------- 1) Using 4 off M3 screws, washers and nuts fit the SO239 Socket to the Box, do NOT forget to fit the Solder Tag also. 2) Fit the multiway switch to the box using the supplied nut and bush. 3) Set the switch so that the ~wipers~ are along the centrelines of the Box as per the ~Hardware.drawing~. 4) Cut the switch spindle to approximately 13mm long. 5) You are now ready to go to ~Part 4:-~. ---------------------------------------------------------------------------- Part 4:- -------- Wiring of the Components:- -------------------------- 1) Fit all of the components as per the ~Hardware.drawing~. 2) Insulate any of the components as required. 3) Feed the ~Audio Input Cable~ through the remaining hole. 4) Connect the cable as per the ~Hardware.drawing~. 5) Insulate the braid as required. 6) Note that tags ~e~ and ~f~ are anchor points only. 7) You are now ready to go to ~Part 5:-~. ---------------------------------------------------------------------------- Part 5:- -------- 1) CHECK and RECHECK ALL of your construction work. 2) Refit the top with the 4 screws supplied with the Box. 3) Fit the control knob to the finished item. 4) The unit is now ready for Testing/Calibration. ============================================================================ Using the Oscilloscope Calibrator Software. ------------------------------------------- Keyboard Controls:- ------------------- (1) Sets the frequency to 1KHz. (2) Sets the frequency to 100Hz (a) or (A) Sets the software attenuator to -20dB below maximum output. Do NOT use this mode unless it is absolutely neccessary, use the mechanical switched ranges instead. (r) or (R) Resets the Output to the Default conditions, (calibrated on an A1200 only). The defaults are, 1KHz Square Wave at 1 Volt peak to peak. (q) or (Q) Quits the program. There are two more hidden keys in the program:- ----------------------------------------------- The ~SPACE~ bar will also Quit the program. (H) That is ~SHIFT h~, Sets the frequency to 10KHz Square Wave. The amplitude may NOT be accurate so therefore the key is not shown on the window. However the frequency IS very accurate for all the AMIGAS. ---------------------------------------------------------------------------- The mouse is optional and can be used to Quit the program or move the window to the background. It does NOT need to be connected for normal operation of the program. ============================================================================ Calibration of the device:- --------------------------- 1) The only test that can be done is with ANY Audio Amplifier. 2) Switch OFF the AMIGA and Amplifier and read the ~Warning~ file. 3) Connect the PHONO/RCA plug of the Oscilloscope Calibrator to the Left Channel Audio Output Socket of the AMIGA. 4) Connect a blank PHONO/RCA plug to the Right Channel Audio Output Socket of the AMIGA. 5) Connect the Output Cable PL259 plug to the SO239 socket of the Calibrator. 6) Connect the Output Cable BNC plug to the Input of ANY Audio Amplifier using a suitable connecting cable or adaptor. A typical adaptor can be obtained from MAPLIN, part number FE88V, (BNC female to PHONO/RCA plug). 7) Set the Audio Amplifier's volume to minimum, and to the correct Input source. 8) Set the Calibrator's Attenuator switch to maximum output, (fully anti-clockwise). 9) Switch ON all of the equipment. 10) Start up the ~Scope_Calib~ software. 11) Adjust the Audio Amplifier's volume for a normal listening level. 12) Switch the Attenuator up or down and listen to the large changes in the volume from the speaker(s). 13) Press ~1~ or ~2~ to hear the frequency changes from the speaker(s). 14) Try the other keys to check that they also work. 15) If all is well, switch OFF all of the equipment and disconnect any of the hardware. ---------------------------------------------------------------------------- Limitations as to use:- ----------------------- Because of the limitations of the AMIGA'S Audio Output the Square Wave will not be as good as a professional Oscilloscope Calibrator. However it is infinitely better than NO calibrator at all and will successfully set up the next project, the Digital Storage Oscilloscope, along with the batteries that you should have for calibrating some of the previous projects. Other Information:- ------------------- In this drawer is an ~iff~ file of the provisional front end for the Digital Storage Oscilloscope. It is called ~Scope_Front_End.iff~ and will require image displaying software to view it. It is a standard 320x200x32 (NTSC) Lores iamge. I have included a project icon with a default viewer called ~Display~. You may change this default viewer and its path to suit yourself. ~Display~ is NOT in this archive. Please let me know via Email whether you like this Front End or not. ---------------------------------------------------------------------------- Using the ~Drawings~ program:- ------------------------------ Important:- ----------- This program requires Workbench 2.xx or greater to run. ------------------------------------------------------- To view any of the construction drawings start up the ~Drawings~ software. You will see a requester with all of the relevant drawings inside it. Double click on the required drawing and it will be displayed. (r) or (R) will bring up the requester again for another drawing. Any other key will Quit the program. For Workbench 1.3x users:- -------------------------- Do NOT run the ~Drawings~ software, instead open up the ~Drawing~ drawer and view the files using an ~iff~ image viewer. All of the ~?.drawing~ files are standard (NTSC) 320x200x2 Lores IFF files. The icons for the ~?.drawings~ are project icons and I have used ~Display~ as the default image viewer. ~Display~ is NOT in this archive. You may change the default viewer and its path to suit yourself. ---------------------------------------------------------------------------- What it is used for:- --------------------- Refer to the ~Examples.drawing~ for all of the following information. The circuit shows a passive network of resistors and capacitors. It is a general circuit for the input of a Vertical Deflection Amplifier of any random analogue Oscilloscope and will be used in the next project. R1 and R2 form a potential divider. TC1, C1 and Cx form the total capacitance across R1, C2 and Cy form the total capacitance across R2. Cx and Cy are both unknown stray values in the range of 1 to 200 Pica-Farads. To obtain some form of frequency compensation the Time Constant (TC1+C1+Cx)xR1 must be the same as (C2+Cy)xR2. We have assumed that there are no stray inductances in the passive network. The variable capacitor TC1 is adjusted to give the best possible Square Waveform from an Oscilloscope Calibrator. If TC1 is too large then the waveform will look like box number (1). If TC1 is too small then the waveform will look like box number (2). However if TC1 is correctly adjusted then the waveform will look like box number (3). This Oscilloscope Calibrator project is set to give a square wave at a specific frequency and with a specific amplitude, and each range of the Digital Storage Oscilloscope's Vertical Amplifier will be adjusted to give the shape in the box number (3). Also the frequency will be used to set up the Timebase ranges. ---------------------------------------------------------------------------- Using the Oscilloscope Calibrator:- ----------------------------------- 1) Switch OFF the AMIGA and read the ~Warning~ file. 2) Connect the PHONO/RCA plug of the Oscilloscope Calibrator to the Left Channel Audio Output Socket of the AMIGA. 3) Connect a blank PHONO/RCA plug to the Right Channel Audio Output Socket of the AMIGA. 4) Connect the Output Cable PL259 plug to the SO239 socket of the Calibrator. 5) Connect the Output Cable BNC plug to the ~Y~ input of an Oscilloscope. 6) Set the Oscilloscope's Vertical Range to 1 Volt peak to peak. 7) Set the Calibrator's Attenuator switch to maximum output, (fully anti-clockwise). 8) Switch ON the AMIGA (and the Oscilloscope if required). 9) Start up the ~Scope_Calib~ software. 10) Adjust the relevant variable capacitor(s) in the Vertical Amplifier to give the best possible Square Waveform. 11) Switch the Attenuator to give a different output and do the same for the other ~Y~ ranges. 12) Use the frequency output to set up the Horizontal Timebase speeds. 13) When finished switch OFF all of the equipment and disconnect any of the hardware. ---------------------------------------------------------------------------- Acknowledgements:- ------------------ First of all many thanks to my wife Tricia who allows me to spend many hours on my computers. Also to David Benn and Herbert Breuer for the ACE/AIDE combination supplied on an AMIGA FORMAT floppy disk which made it easy to compile this program. Also to Laurence J Greatorex for giving these a shakedown on his A1200 with a Turbo LC '030 accelerator board and 32MB of fast ram, also to Bob Eva for testing on his A1200 setup, with a total of 10MB of memory and also to Nathan Shepherd with his absolutely standard A500 without a mouse. To the other people that have given any of these projects a rigorous testing. And finally to anyone else who I may have neglected or forgotten. ---------------------------------------------------------------------------- Mr Barry Walker, 70 King George Road, Loughborough, Leicestershire, LE11 2PA, England. Email to:- 106161.3245@compuserve.com or wisecracker@tesco.net BYE..... ----------------------------------------------------------------------------