Coil Winder It Winds and Counts

Transcription

1 Coil Winder It Winds and Counts By Rolf Gerstendorf (Germany) Many low frequency inductors used in lon and medium wave receiver desin require a few hundred turns of wire. Windin the coils by hand can be troublesome, especially if you lose count alon the way. This simple coil winder is easy to build and spins the coil former clockwise or anticlockwise while keepin track of the turns and displayin the exact value with a resolution of one tenth of a turn. This coil winder desin, as the name suests, is used to wind coils. It keeps track of the number of turns and the direction of rotation with the help of an encoder disc mounted on a motor shaft. The disc is divided into ten sections alternatin black and white. Two opto-sensors are used to reister the turn of the disc in either direction. Clockwise rotation of the motor shaft increments the value shown on an LED turns-counter display while counter-clockwise rotations decrement the value. Hardware The circuit diaram shown in Fiure can be divided into five sections: First is the display consistin of four 7-sement LEDs. Next is a rotation impulse enerator (both the display and impulse enerator connect to the microcontroller). A DC motor controller and a voltae reulator. Any intellience in the operation of this coil winder is provided by the ATmea8P (IC) microcontroller which is clocked from its internal 8-MHz clock sinal. Its main function is to count rotations of the motor axle in both clockwise and counter-clockwise direction and to control the four 7-sement LEDs. The display can show a maximum of turns. The circuit around the two reflective optosensors type CNY-70 (IC and IC) enerates the rotational turns count and direction of rotation for the controller. The opto-sensors are positioned next to each other where they illuminate the black and white encoder disc. elektor post Project No. 7

2 When liht from the opto-sensors internal LED hits a white reion of the disc it is reflected back to the phototransistor which conducts anulls the output sinal and the microcontroller pin to round. The black reion absorbs liht so when this part of the disc is under the opto-sensor the phototransistor does not receive any reflected liht and turns off. The correspondin controller input will now be pulled Hih by the pull-up resistors R or R. different the turns counter is decremented. The display is made up of four 0. inch 7-sement LED displays with common cathodes. All seven sements from the displays LD to LD are connected in parallel to controller outputs PB0 to PB6. Pins PC0 to PC drive the common cathodes of the four display characters via transistor buffers T to T. The decimal point pin on display LD is connected to the supply rail via resistor R so that the display has the format The disc has five white and five black sements which ives 0 chanes of liht level per revolution. The software monitors the chane of input level from IC at pin PD and uses it to chane the count value. At the same time it checks the output level of IC (pin PD6), if both inputs are at the same state the turns-counter is incremented, if they are The coil winder uses a N78 V DC motor from Iarashi []. It weihs just 70 and its low-cost makes it a favorite in the modelbuildin community. The motor achieves maximum efficiency (66.7 %) with a load current of. A (. W) runnin at,000 rpm. In this application we won t be ettin anywhere near that speed (could lead Fiure. The coil winder circuit. C C 00n IC 00R IC CNY70 D N08 R R R6 R 0k 00R 0k R n A PB0 PB PB PD0 PB PD IC PB PD PB PD PB6 6 PD PB7 PD PD6 ATMEGA8-PU PD7 PC0 PC PC PC PC AREF VE R8 PC PC6 GND GND 8 W Sb M M TIP R 0R R 0R R 0R R 0R R 0R R6 0R R7 0R 7 a 0 7 a 0 7 a 0 7 a 0 LD LD LD LD T R8 LM780 R T R9 T R0 R 0 T P 0k R7 Sa T TIP7 B C E C E B C 00n C 00u 6V LM780 IC VE C 00u 0V D N08 K 08- elektor post Project No. 7

3 to combustion of your diital extremities!), the technical data indicates that this motor can supply sufficient torque (8.7 mnm) for the application here. Control of the motor speed is completely independent of the microcontroller and can be rearded as fairly basic. Power to the motor is supplied by the Darlinton-transistor T, the 0 K pot P simply controls the base current to T to chane the motor speed. You just need to select the motor speed as required. For thicker wire use a slower motor speed. The motor can draw 0 A when it stalls so resistor R8 is used to limit the maximum current. The three position ON-OFF-ON DPDT switch S is used to chane the motor s direction of rotation. The N08 diode D is rated at A to provide the freewheel function. The circuit is powered from a V wall adapter type power supply which connects to socket K. Diode D protects the circuit from a reverse polarity power connection. The motor is powered directly from this supply while the rest of the circuit is powered from a stabilized V supplied by the voltae reulator IC. Software The software was written in C usin AVRstudio. The proram source file and the compiled version of the proram can be downloaded for free from []. Fiure shows the fuse settins used and how they are shown when prorammin in AVR-Studio. The main proram consists of two functions: Display_se-Function This function takes the value of count as an arument, separates the value into individual numbers and displays them on the 7-sement LEDs. ISR0-Routine PD is used as an interrupt input. The interrupt service routine will be called at every status chane of PD. It compares the value on input PD6 with PD and increases the turns count (if PD6 is the same) or decrements (if PD6 is not the same) the count value. Mainfunction (Hauptfunktion) This is the main function which defines the I/O pin data direction, takes care of initialization, enables the interrupts and calls the Display_se-Function. The Mechanics All components, electrical and mechanical are fitted to the PCB (Fiure ), which was produced usin the free PCB software called Desinspark PCB []. The layout and software files can be found on the project pae []. The PCB layout allows it to be fitted into a basic enclosure or project box. Holes are required to accommodate the pot P and switch S. A cutout is also required for the four displays (fitted to the upper side of the PCB). A hole is also necessary in the lihttiht enclosure for the motor shaft. Header sockets are fitted to the PCB to mount the 7-sement displays. The two opto-sensors are also fitted to the upper side; all the other components are mounted on the reverse side of the doublesided PCB. Transistor T must be fitted with an effective heat sink. The encoder disc is divided up into ten sections and then colored black and white. The easiest option is to make a photocopy of Fiure ; this will ive you a correctly sized 0 mm diameter disc. It can be lued to a 0 mm diameter scrap piece of PCB. Ensure everythin is symmetrical around the center hole to avoid vibrations when the motor Fiure. The microcontroller fuse settins. elektor post Project No. 7

4 COMPONENT LIST Resistors R R7,R = 0Ω R8 R,R7 = Ω R,R = 0kΩ R,R6 = 00Ω R8 = Ω W P = 0kΩ potentiometer Capacitors C,C,C = 00nF C = 00µF 0V C = 00µF V Semiconductors D,D = N08 LD LD = 7-Sement-display, 0., common cathode, e,. Kinbriht SC0-EWA T = TIP7 T T = IC = LM780 IC = ATmea8-PU (Atmel), prorammed, Elektor Store # 08- IC,IC = CNY70 (Vishay) Miscellaneous S = tole switch, DPDT (TE Connectivity A0SYZQ0) K = -way PCB screw terminal block, mm pitch Pinheaders, 0. pitch -V motor type N78-0-G- RS8SH (Iarashi), Conrad Electronics # 0 Propeller-Hub-Reel for.mm spindle (08), Conrad Electronics # PCB, Elektor # 08- [] spins up. The size of the central hole will be overned by the method used to attach it to the motor axle. The motor itself is fixed to the PCB usin two M x 0. x mm screws as shown on the layout. Make sure that the screws don t extend any further than mm into the motor housin. There are a number of ways that the disk and coil former can be fitted to the. mm diameter axle []. For this example we chose an electric fliht propeller hub. The disc can be lued directly onto the shaft. Whichever method you use don t foret that the distance between the opto-sensor and the disc surface should be approximately mm. In the case where the motor is not fixed to the PCB (you could, for example use an electric 08- Fiure. All components, includin the motor are fitted to the double-sided board. Fiure. : template for the encoder disc. elektor post Project No. 7

5 drill to wind the coil) the opto-sensors will also need to be mounted off the PCB. However you confiure your setup it is important to remember firstly, that a multi-core screened cable should be used for wirin between the opto-sensors and PCB. This helps reduce the chance of pickin up interference sinals in the cable which may lead to incorrect values displayed on the turns counter. Secondly, make sure that the opto-sensor is properly shielded from any external stray liht. (08) Web Links [] [] [] [] elektor post Project No. 7