File:20120801 184016.jpg

2012-08-01T19:12:41Z

Peejaywk:

RaspberryPi Buffer Board

2012-08-01T17:34:05Z

Peejaywk: /* Schematic */

[[Category:RaspberryTortoise]]

To interface the RaspberryPi to the BigTrak motor controller and encoders it was decided to build a buffer board. The purpose of the buffer board is to protect the RaspberryPi from being over driven and also allows the RaspberryPi to drive outputs at a higher current level.

== Schematic ==
The buffer board design is based on the [http://www.scribd.com/doc/88286916/Gertboard-Overview Gertboard] and consists of two SN74AC244N Octal Buffers. The board has 8 outputs and 7 inputs.

[[File:BufferBoard.jpg|300px|RaspberryPi Buffer Board]]

{| class="wikitable" style="text-align: center; width: 300px; height: 200px;"
|+ Output Pinouts
|-
! scope="col" | J2 Pin Number
! scope="col" | Name
! scope="col" | RaspberryPi Name
|-
! scope="row" | 1
| 3V3 || 3V3
|-
! scope="row" | 2
| 0V || 0V
|-
! scope="row" | 3
| Output 1 || GPIO 0
|-
! scope="row" | 4
| Output 2 || GPIO 1
|-
! scope="row" | 5
| Output 3 || GPIO 4
|-
! scope="row" | 6
| Output 4 || GPIO 17
|-
! scope="row" | 7
| Output 5|| GPIO 18
|-
! scope="row" | 8
| Output 6 || GPIO 21
|-
! scope="row" | 9
| Output 7 || GPIO 22
|-
! scope="row" | 10
| Output 8 || GPIO 23
|-
|}

{| class="wikitable" style="text-align: center; width: 300px; height: 200px;"
|+ Input Pinouts
|-
! scope="col" | J3 Pin Number
! scope="col" | Name
! scope="col" | RaspberryPi Name
|-
! scope="row" | 1
| Input 1 || GPIO 24
|-
! scope="row" | 2
| Input 2 || GPIO 10
|-
! scope="row" | 3
| Input 3 || GPIO 9
|-
! scope="row" | 4
| Input 4 || GPIO 25
|-
! scope="row" | 5
| Input 5 || GPIO 11
|-
! scope="row" | 6
| Input 6 || GPIO 8
|-
! scope="row" | 7
| Input 7|| GPIO 7
|-
! scope="row" | 8
| N/C ||
|-
! scope="row" | 9
| N/C ||
|-
! scope="row" | 10
| N/C ||
|-
|}

== References ==
#[http://www.scribd.com/doc/88286916/Gertboard-Overview Gertboard Overview]

RaspberryPi Buffer Board

2012-08-01T17:28:48Z

Peejaywk:

RaspberryPi Buffer Board

2012-08-01T17:15:10Z

Peejaywk: /* Schematic */

RaspberryPi Buffer Board

2012-08-01T17:14:53Z

Peejaywk:

File:BufferBoard.jpg

2012-08-01T17:13:33Z

Peejaywk: Buffer Board

Buffer Board

2012-07-14T10:08:36Z

Peejaywk: /* Encoder Circuit */

[[Category:RaspberryTortoise]]

This page documents the circuit inside the new Big Trak.

== Motor Control ==
Big Trak contains a H-bridge Motor Control circuit that makes it possible to rotate the motor in both direction from a single power source. In this case it is 4.5volts. The circuit diagram below shows the left hand side motor control circuit. The circuit is the same for the right hand side.

[[File:mototcontrol.jpg|800px|Big Trak Motor Control Circuit]]

To make the motor rotate in a forward direction a positive voltage is applied to the forward input whilst the reverse input is pulled low. With these inputs transistors Q5 and Q13 will conduct allowing current to flow through the motor. To reverse the motor direction a positive voltage is applied to the reverse input while pulling the forward input low. This will cause Q4 and Q12 to conduct and hence will reverse the current flow through the motor.

'''Note Do not apply a positive signal to both inputs at the same time.'''

Using this circuit it should be possible to control the speed of the motors by pulsing the inputs (PWM Control).

From the Big Trak circuit it is not possible to determine the identities of transistors Q8 and Q10 as they are very small surface mount devices.

=== Replacement Options ===
As the Big Trak circuit will eventually be removed it will be necessary to make a replacement motor control circuit. This web site [http://www.electronics-tutorials.ws/blog/h-bridge-motor-control.html] has some useful information and also suggests an H-Biridge motor control IC that could be used instead of discrete components. This is the National Semiconductors [http://www.ti.com/lit/ds/symlink/lmd18200.pdf LMD18200]. This is probably a bit of an overkill but it's a start.

#[http://www.sparkfun.com/products/9457 Motor Driver 1A Dual TB6612FNG]
#[http://www.active-robots.com/motor-driver-1a-dual-tb6612fng.html Motor Driver 1A Dual TB6612FNG UK source]

== Encoder Circuit ==
Big Trak has a simple encoder system for measuring how far it has travelled. The circuit diagram for this is shown below. Not 100% sure this is correct (Needs checking).

[[File:encodercircuit.jpg|400px|Big Trak Encoder Circuit]]

== References ==
#[http://www.alldatasheet.com/datasheet-pdf/pdf/419843/SECOS/D882S.html D882S Datasheet]
#[http://www.alldatasheet.com/datasheet-pdf/pdf/419598/SECOS/B772S.html B772S Datasheet]