The first My Block, LiftPen, is a simple one. The Printer uses it to lift the pen from the paper so that it can move the pen to a different place on the paper without drawing a line as it moves. You need just one Motor block to accomplish this, but turning it into a My Block makes the action easier to perform frequently. Configure this Motor block as shown in Figure 16-8 (left side), and turn it into a My Block called LiftPen as shown in Figure 16-8 (right side). Be sure to select a few icons for this block to distinguish it from the LowerPen block you’ll make next.

The LowerPen block lowers the pen so that it touches the paper. To do this, the block first instructs motor C to lower the pen for a certain amount of time. This action firmly presses the pen against the paper, deliberately applying too much pressure. The motor then reduces the pressure by raising the pen for a moment. Configure the blocks that perform this process as shown in Figure 16-9 (left side), and turn them into a My Block called LowerPen, selecting a few icons for the block as shown in Figure 16-9 (right side).

Figure 16-8. A single Motor block (left) comprises the LiftPen My Block (right).

Figure 16-9. Two Motor blocks (left) comprise the LowerPen block (right).

Figure 16-10. Four blocks (left) comprise the ResetHorizontal My Block (right).

For accurate printing, the Printer should know where it is writing on the paper. To determine its position, the Printer always starts printing on the top left of the page and thereafter tracks its position relative to that starting point.

Now you’ll make two My Blocks that position the pen at the upper-left corner of the paper. Begin by creating the ResetHorizontal My Block, which moves the horizontal module with the pen all the way to the left of the page. The module stops moving left when it presses the touch sensor and then moves to the right slightly to release some pressure. The rotation sensor in the horizontal motor resets at this point so that the Printer knows the pen is in the starting horizontal position.

Configure the blocks to do this as shown on the left of Figure 16-10, turn them into a My Block called ResetHorizontal, and select a reset icon for it as shown on the right of Figure 16-10.

The ResetVertical My Block moves the paper in the machine so that the pen is at the top of the page. When you insert a sheet of paper into the Printer’s drawer, this My Block should move the paper into the machine until the color sensor detects white, at which point the machine knows that paper is present. Next, the block draws the paper further into the machine in order to release stress from the paper. Finally, the block pushes the paper back out a little so that the paper sits in the correct position. The rotation sensor in the vertical motor resets at this point so that the Printer knows that the sheet of paper is in the starting vertical position.

Configure the blocks to perform the previous action as shown on the left of Figure 16-11, turn them into a My Block called ResetVertical, and select a reset icon for your My Block as shown on the right of Figure 16-11.

The Eject My Block ejects the paper. It runs until the color sensor detects that the paper is no longer present, at which point the motor moves for another second to make sure that the paper is released and then stops. You place the LiftPen block inside the Eject block to make sure that the Printer won’t accidentally draw a line all the way across the paper.

Configure the blocks to perform this action as shown on the left of Figure 16-12, turn them into a My Block called Eject, and select the red stop sign for this My Block as shown on the right of Figure 16-12.

Figure 16-11. Eight blocks (left) comprise the ResetVertical My Block (right).

Figure 16-12. Five blocks (left) comprise the Eject My Block (right).

The last two My Blocks you’ll create move the pen on the paper. You can use these blocks while the pen is lowered (a line is drawn) or raised (no line is drawn).

If the horizontal motor rotates forward a certain number of degrees, the horizontal module moves to the right. Running the motor in reverse will move the module to the left. You’ll create a special My Block for this action that can accept input values (an amount of degrees), allowing you to configure the block with a configuration panel. Positive values move the module to the right, and negative ones move it to the left. Create the Horizontal My Block by following the steps in Figure 16-13 to Figure 16-15.

Figure 16-13. Use the Constant block to generate a data wire that acts as an input for the Compare block. The Compare block checks whether the value is greater than 0. If it is, the direction is forward; otherwise, the direction is backward. The Compare block also transfers the number of degrees to the Motor block. A Wait block at the end makes sure that the motor has fully stopped when the My Block finishes.

Figure 16-14. Select the latter three blocks as shown (left), and then convert them into a My Block called Horizontal. The result should be the figure shown on the right. Be sure to choose an appropriate icon for your My Block, such as the two horizontal arrows shown here (right).

Figure 16-15. Delete the Constant block, and hide the Horizontal block’s data hub. You have now created a My Block with a configuration panel.

Figure 16-16. Configure these four blocks as shown.

You’ll now repeat the steps from the Horizontal My Block to create a similar block called Vertical, which controls the position of the paper in the machine. A positive value pulls the paper into the Printer, and a negative one pushes the paper away from the Printer. Create the Vertical My Block now by following the steps in Figure 16-16 and Figure 16-17.

Figure 16-17. Select the latter three blocks, turn them into a My Block called Vertical (left), and select a vertical arrow as an icon for your block (right). Also, delete the Constant block, and hide the My Block’s data plug.

To test the My Blocks, you’ll create a program that uses each of them. See Figure 16-18 for the overall setup of your program, and see Figure 16-19 for the blocks you’ll place in the middle of your program.

Run the program, and insert a sheet of paper into the Printer’s drawer (see Figure 16-1) when the vertical motor begins to turn. If running the test program gives a result like the one shown in Figure 16-20, skip to Creating the Final Program. If this is not the result, go to Troubleshooting the Printer.

Figure 16-18. The basics of a program for the Printer

Figure 16-19. The blocks in the middle of the test program

Figure 16-20. The expected result of the test program. The tilted line is the result of a Horizontal block and a Vertical block running in parallel at the same time.

Once you insert the paper into the machine and the ResetVertical My Block has finished running, the uppermost part of the sheet in the machine should lie completely flat, resting on the beam to which you’ve added a strip of tape. If the paper is not lying flat because it’s slightly crumpled or creased, the Printer won’t be able to draw properly. Use a fresh sheet of paper, or try using thinner, less stiff paper.

In some instances, the pen won’t write because not enough pressure is being applied or because it doesn’t touch the paper. If the pen sits above the paper by more than 0.5 cm (0.2 inches), check the building instructions in 7.

If the pen is close to the paper but not close enough or if not enough pressure is applied to the pen, the solution lies in the program. In the LowerPen My Block, modify the Duration setting in the first Motor block, which is currently set to 0.40 seconds. Try 0.45 seconds or longer if necessary.

The pen may press too hard on the paper, making it impossible to move the paper vertically. To fix this, see The Pen Doesn’t Write above, and change the Duration to a number less than 0.40, such as 0.35 seconds.

In areas of very bright sunlight, the color sensor cannot detect the paper sheet properly because it reads white even when no paper is present. When this occurs, the ResetVertical My Block will behave incorrectly. To fix this, move the Printer to an area with less light and try again.

When the paper is moving backward into the machine so that the pen can write on the bottom portion of the paper, the paper can sometimes catch on motor A’s cable. To prevent this, twist, tuck, or otherwise move the motor’s cable out of the paper’s path.