fig1 shows a microprocessor 66 interconnected to control mechanism 21 through an interface device 60 . a memory device 70 is also connected to the microprocessor 66 . within the control mechanism 21 is a switch 20 to control its output through leads 30 , 30a , 30b , 30c , etc . a pair of power supplies 16 and 18 are shown supplying power to two different modes of operation of the control mechanism 21 , namely the &# 34 ; read &# 34 ; mode and the &# 34 ; write &# 34 ; mode . a timing mechanism 22 controls the output of the source 16 to the write mode . the leads 30 etc . connect to a plurality of styli 40 which are positioned ( for writing and reading ) over a piece of electrosensitive material 50 . the particular material shown has a paper layer 50 , an ink layer 52 and an aluminum layer 54 . a ground contact 12 on the conductive layer 54 is interconnected to the control device 21 by lead 14 . in operation when switch 20 is in the write mode , power supply 16 generates a dc or ac signal ( up to radio frequency range ) of magnitude from about 40 to about 100 volts . when switch 20 is in the &# 34 ; read &# 34 ; mode the power supply 18 generates a dc output in the 5 to 16 volt range . power supply 18 can be generated by stepping down the output of supply 16 . in one embodiment of the present invention , the output supply 16 generates a positive output to leads 30 , 30b , etc . and a negative output to leads 30a , 30c , etc . in such an embodiment positive and negative output are relative terms , i . e ., one stylus may be positive and its neighbor ground or neutral . in order for the device 21 to control reading or writing of much significance , some device for causing relative motion between the stylus 40 and the paper 50 must be provided . several printers are commercially available which show such operation , one is the product of sci , inc . of huntsville , alabama identified as model 1100 , another is the product of axiom corporation of glendale , california , identified as model ex800 . the sci printer is a rotary printer in which the styli rotate and the paper is propelled past the styli . the detailed function of this device is described in u . s . pat . no . 3 , 998 , 315 and in u . s . pat . application ser . no . 611 , 785 filed sept . 9 , 1975 . whatever method is chosen the paper feed 82 is controlled by a device 90 . as the sci device indicates both styli and paper can be in motion and the present invention encompasses the composite motion of the styli and paper . fig4 and 5 show two different embodiments of styli in two different configurations . the styli 42a etc . shown in fig4 have rectangular shapes with the longer dimension in the direction of paper motion . the styli 142a shown in fig5 have oval tips with the longer dimension at an acute angle to the direction of paper motion . an angle of about 45 degrees appears to give good results . the styli 42a etc . are shown in staggered array with the longer dimension large enough for the styli tips to touch or overlap if the &# 34 ; stagger &# 34 ; were eliminated . the stagger can be thought of as a tilted and skewed array of styli . the skewing or twisting of the styli as shown in fig4 and 5 give additional strength to the array which is important during the read operation . the styli 142a etc . shown in fig5 are shown in an oblique array in which the styli tips would touch or overlap if the oblique angle were reduced to zero . the styli tips as shown in fig5 would touch or overlap if the styli 142a , etc , were rotated in a clockwise direction . although the fig4 styli 42a etc . have rectangular tips and the fig5 styli 142a etc . have oval tips , the two shapes may be interchanged to give four different styli embodiments . shown in fig5 b , styli with round or cylindrical tips are well known . to improve the performance of such styli during the read mode it is useful to twist the styli as shown in fig5 a . the twist permits the styli to flex in the proper direction and therefore ride more smoothly over the surface to be written or read . the twist is applied about midway in the length of the styli . to enable the styli shown in fig4 to write a straight line the activation of the styli in the write mode is appropriately staggered by the timing device 22 shown in fig1 . in operation the styli are maintained in very light sliding contact with the electrosensitive material 50 . the write voltages of between 40 and 100 volts ac or dc are applied for about 100 microseconds . during the write cycle the aluminum layer 54 is vaporized exposing the underlying ink layer 52 . this allows the document to be humanly or machine readable . the read and write speeds of the device are substantially equal but the read voltages are in the 5 to 16 volt range . the read voltage may be ac or dc and may be much higher than 16 volts but produce a low current flow . an electrosensitive material 50a is shown in fig6 having horizontal synchronization marks 56a , vertical synchronization marks 56b and timing tracks 58a , 58b and three colors of printing a , b , c , written thereon . the timing tracks 58a , 58b are useful for synchronous reading . the tracks 58a , 58b can be omitted and the reader can function synchronously . the three color a , b , c is achieved by using three different inks 52a , 52b , 52c under the aluminum layer 54a . the timing tracks 58a , 58b are normally printed when the data on the paper is printed . the horizontal and vertical synchronization marks 56a and 56b may be printed by the device or by a separate printer . the horizontal lines 56a give accurate vertical position and the vertical lines 56b give accurate horizontal position . the number of synchronization lines and timing marks created will depend on the number of styli per head . a common configuration is a 7 stylus array . in such an array 6 bars will carry data allowing for 64 characters and one bar will be parity . when the styli &# 34 ; fire &# 34 ; across to adjacent styli 6 bars will create five lines of information . when the styli &# 34 ; fire &# 34 ; to ground six bars can be created by 6 styli . a compound system of evaporating the conductive layer from stylus to stylus and from stylus to ground has been found to work effectively also when using a seven stylus head and bar code character can be written using five styli for writing and two styli for spacing . when writing graphics the two spacing styli are able to draw continuous lines . the styli may create as many lines on the electrosensitive material as they are controlled to do . for reading or writing synchronously a single stylus can either read or write the timing track . when a user wants to read from a previously written document 50 ( such as a check or business form ), he places the document to be read in the input hopper 110 and sets the switch 20 to the read mode . the input - output device moves the document from the hopper into position under the read - write heads . this reader detects the horizontal , vertical and timing marks and makes the appropriate adjustment of the position of the document feed device or the read heads depending on the type of reader . the document &# 39 ; s relative movement past the read head continues . in the read mode the styli are energized through the interface device 60 to a low voltage range . the styli , in light contact ( about 1 gram ) with the document , sense a change in resistance , conductance or capacitance as the styli move from aluminum to ink back to aluminum on the written document . changes in the resistance , conductance or capacitance are changes in the electrical properties of the electrosensitive material . the read head senses the bar code writing resistively conductively , or capacitively . the interface device 60 converts the sensed data to appropriate digital form for transmittal to the microprocessor 66 . the microprocessor 66 is set to either display the data received on a crt 112 or to transmit it to local or remote memory . at the completion of the read cycle , the document is deposited in the output hopper 114 for later removal by the user . when a user wishes to write on a document he loads the document into the input hopper 110 and sets switch 20 to the write mode . the user then selects the source of the writing . he may write from information in local or remote memory ( not shown ) or from information supplied through a keyboard 116 or from information from another document in a second input hopper i . e ., input - output devices operating in tandem . when input - output devices operate in tandem they can function as facsimile machines with the important difference that output in digital form can be fed directly to a processor or memory . whatever the source of the data to be written , the operator must either through program or keyboard instruction direct the printer to write in machine readable or humanly readable form or both . assuming , for illustration that both modes of writing are chosen and that information from local memory is to be written , the user enters the appropriate information through the keyboard . the document is moved from the input hopper to the writing heads ( or the writing heads are moved over the input hopper ). the horizontal and vertical synchronization tracks ( if present ) are sensed and then the heads shift to write automatically . a timing track ( for synchronous reading ) is immediately generated for later use during the read mode . the program controlling the microprocessor 66 directs the heads 40 to write in code or alpha - numeric in the appropriate place on the document . the digital data in the microprocessor memory is converted by the interface 60 which includes a pio and an a to d converter into a proper analog form for transmission to the write heads and styli . the output voltage of about 40 to 100 volts for about 100 microseconds is fed to a particular stylus whenever it is desired to make a mark on the document . this energy is sufficient to vaporize the upper layer and expose the underlying layer of the document . the styli may be energized relative to ground or relative to adjacent styli depending on the program in the microprocessor and the configuration of the interface . the timing for energization of the styli will depend on the position of the stylus array and on what is to be written . when the write cycle is complete , the document is moved to an output hopper or the write head has returned to its rest position . in either read or write modes an automatic document feed allows the stacking of documents .