Counter Display, PICO PI zero

Build a simple counter display for counting the robot running test. New Piezoresistive sensor, more simple installation.

The counter display is designed for counting the number of turns Picobot runs. The circuit is built with a Pi zero board, a 4-digit display and a 74HC14 chip. The sensor is a homemade contact ON/OFF using plastic sheet and aluminum foil. The display is made of two chips, a 2281BS common anode seven segment display. The segment pins are connected from GP0 to GP7. The common pins are connected from GP12 to GP15 through the four 74HC14 gates. Display is multiplex scanning and current limitted is done by software.

The sensor is placed on the black line. When the bot passes, the contact is closed. The display module will detect the logic changes at GP8 and increment the number of turns.

The sensor is made of a thin plastic sheet. Bend the top sheet to make the slope. Use aluminum foil to be an inductive sheet for both layers, top and bottom. Then wire them to J2. On the top layer, have the white paper and back tape as shown above. Here is the cross-section of how the sensor was made.

The control software was written in BASIC. The PI board uses the MMBASIC interpreter. BASIC program listing is shown below.

REM Counter Meter
REM Count the number of turn of Picobot running
REM Use simple ON/OFF sensor
REM Maximum 9999

SetPin gp0, dout
SetPin gp1, dout
SetPin gp2, dout
SetPin gp3, dout
SetPin gp4, dout
SetPin gp5, dout
SetPin gp6, dout

SetPin gp12,dout
SetPin gp13,dout
SetPin gp14, dout
SetPin gp15, dout

Sub led1 d

Pin(gp12)=0 : Pin(gp13)=1 : Pin(gp14)=1 : Pin(gp15)=1

Write_segment d
End Sub

Sub led2 d

Pin(gp12)=1 : Pin(gp13)=0 : Pin(gp14)=1 : Pin(gp15)=1

Write_segment d

End Sub

Sub led3 d

Pin(gp12)=1 : Pin(gp13)=1 : Pin(gp14)=0 : Pin(gp15)=1

Write_segment d
End Sub

Sub led4 d

Pin(gp12)=1 : Pin(gp13)=1 : Pin(gp14)=1 : Pin(gp15)=0

Write_segment d

End Sub

Sub write_segment d

Select Case d

Case 0

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=0: Pin(gp6)=1

Case 1

Pin(gp0)=1: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=1

Case 2

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=1: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=1: Pin(gp6)=0

Case 3

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=0

Case 4

Pin(gp0)=1: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=0: Pin(gp6)=0

Case 5

Pin(gp0)=0: Pin(gp1)=1:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=1:Pin(gp5)=0: Pin(gp6)=0

Case 6

Pin(gp0)=0: Pin(gp1)=1:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=0: Pin(gp6)=0

Case 7

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=1

Case 8

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=0: Pin(gp6)=0

Case 9

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=1:Pin(gp5)=0: Pin(gp6)=0

End Select

End Sub

Sub turn_off_display

Pin(gp0)=1: Pin(gp1)=1:Pin(gp2)=1: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=1

Pin(gp12)=1 : Pin(gp13)=1 : Pin(gp14)=1 : Pin(gp15)=1
Pause (1)

End Sub

Sub scan a,b,c,d

led1 a
Pause (0.1): turn_off_display
led2 b
Pause (0.1): turn_off_display

led3 c
Pause (0.1): turn_off_display
led4 d
Pause (0.1): turn_off_display

End Sub

SetPin gp8, din

n=0

If Pin(gp8)=1 Then n=n+1 : Print n : Pause 1000

m=n

i = n\1000
n = n Mod 1000
j = n\100
n = n Mod 100
k = n\10
l = n Mod 10

n=m

scan i,j,k,l

Pause (5)

Loop

The main program is a forever loop, detecting pin GP8. If pin GP8 is high (contact sensor is closed), then increment the counter N. And delay for 1000ms to debounce the contact. For slower bot running, the delay could be 2000ms. The counter N, maximum 9999, is converted into four digits, i, j, k, l. Subroutine scan will get four digits and write the 7-segment pattern to the display. Current limited is done by regulating with a 10% turn on power for each digit.

Piezoresistive sensor

The new sensor, Piezoresistive element, has been tested. The sensor can be placed on the floor. When the bot is moving on the sensor, the sensor resistance is changed from very high to low resistance. We can interface it to the PI zero ADC using a simple voltage divider with 10k pull-up.

New program with Piezoresistive sensor.

Rem Counter Meter
Rem Count the number of turn of Picobot running
Rem Use Piezoresistive sensor
Rem Maximum 9999

SetPin gp0, dout
SetPin gp1, dout
SetPin gp2, dout
SetPin gp3, dout
SetPin gp4, dout
SetPin gp5, dout
SetPin gp6, dout

SetPin gp12,dout
SetPin gp13,dout
SetPin gp14, dout
SetPin gp15, dout

Sub led1 d

Pin(gp12)=0 : Pin(gp13)=1 : Pin(gp14)=1 : Pin(gp15)=1

Write_segment d
End Sub

Sub led2 d

Pin(gp12)=1 : Pin(gp13)=0 : Pin(gp14)=1 : Pin(gp15)=1

Write_segment d

End Sub

Sub led3 d

Pin(gp12)=1 : Pin(gp13)=1 : Pin(gp14)=0 : Pin(gp15)=1

Write_segment d
End Sub

Sub led4 d

Pin(gp12)=1 : Pin(gp13)=1 : Pin(gp14)=1 : Pin(gp15)=0

Write_segment d

End Sub

Sub write_segment d

Select Case d

Case 0

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=0: Pin(gp6)=1

Case 1

Pin(gp0)=1: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=1

Case 2

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=1: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=1: Pin(gp6)=0

Case 3

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=0

Case 4

Pin(gp0)=1: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=0: Pin(gp6)=0

Case 5

Pin(gp0)=0: Pin(gp1)=1:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=1:Pin(gp5)=0: Pin(gp6)=0

Case 6

Pin(gp0)=0: Pin(gp1)=1:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=0: Pin(gp6)=0

Case 7

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=1

Case 8

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=0:Pin(gp5)=0: Pin(gp6)=0

Case 9

Pin(gp0)=0: Pin(gp1)=0:Pin(gp2)=0: Pin(gp3)=0
Pin(gp4)=1:Pin(gp5)=0: Pin(gp6)=0

End Select

End Sub

Sub turn_off_display

Pin(gp0)=1: Pin(gp1)=1:Pin(gp2)=1: Pin(gp3)=1
Pin(gp4)=1:Pin(gp5)=1: Pin(gp6)=1

Pin(gp12)=1 : Pin(gp13)=1 : Pin(gp14)=1 : Pin(gp15)=1
Pause (1)

End Sub

Sub scan a,b,c,d

led1 a
Pause (0.1): turn_off_display
led2 b
Pause (0.1): turn_off_display

led3 c
Pause (0.1): turn_off_display
led4 d
Pause (0.1): turn_off_display

End Sub

Sub wait_scan

For q=0 To 200
scan i,j,k,l
Pause (5)
Next q

End Sub

Sub update_display

m=n

i = n\1000
n = n Mod 1000
j = n\100
n = n Mod 100
k = n\10
l = n Mod 10

n=m

End Sub

SetPin gp26, araw

n=0

Print Pin(gp26)

If Pin(gp26) <2000 Then n=n+1 : update_display : wait_scan

scan i,j,k,l

Pause (5)

Loop

Pin PG26 (ADC0) is set to analog RAW readings. The main program prints the ADC0 value. When the value is less than 2000, i.e. the bot makes pressure on the sensor, the variable N is incremented.

See the sample video below.

Download

Schematic

Source code in BASIC program , BASIC Interpreter for PI zero board

More technical information, please contact Wichit Sirichote, wichit.sirichote@gmail.com