Directed Perception Pan–Tilt Unit (PTU)

This page describes how to connect and control the Directed Perception PTU-46-17.5 Pan–Tilt Unit on Ubuntu 22.04 using a USB-to-RS232 adapter.

The PTU is used to position the ZED 2i camera over the workspace.

---

1. Identify the USB Device

Plug in the PTU adapter and check which serial device was created:

dmesg | grep ttyUSB

Example output:

usb 3-2: ch341-uart converter now attached to ttyUSB0

This means the PTU is available at:

/dev/ttyUSB0

If you unplug and replug the adapter, a new /dev/ttyUSBX device should appear.

---

2. Add Serial Port Permissions

If you do not have permission to access /dev/ttyUSB0:

sudo usermod -a -G dialout $USER

Then log out and log back in.

---

3. Connect to the PTU

Install screen if needed:

sudo apt install screen

Connect to the PTU:

screen /dev/ttyUSB0 9600

If you cannot see what you type:

Ctrl + A → : → echo

To exit screen:

Ctrl + A → \ → y

---

4. Testing Communication

After connecting, try typing:

POS

If the PTU responds with:

! Illegal argument

This is actually good — it means the PTU is responding, but the command format is wrong.

---

5. Correct PTU Commands

The PTU requires axis-specific commands.

Command	Description
PP	Pan position query
TP	Tilt position query
PP593	Move pan to +10°
TP-297	Move tilt to -5°
PS 1000	Set pan speed
TS 1000	Set tilt speed
R	Reset / Home

Example commands:

PP
TP
PP593
TP-297

---

6. Units and Motion

The PTU uses counts, not degrees.

Approximate conversion:

59.3 counts ≈ 1 degree

Examples:

Degrees	Counts
10°	593
30°	1780
-5°	-297
-10°	-593

---

7. Typical Setup Position

In the experiment, the PTU tilt is typically set with:

TP-800

This positions the camera correctly over the workspace.

---

8. Serial Communication Notes

Setting	Value
Baud rate	9600
Data bits	8
Parity	None
Stop bits	1
Mode	8N1

Important notes:

• Commands are case-sensitive
• Commands must end with carriage return
• If you see ! Illegal argument, the command format is incorrect
• PP and TP without numbers return the current position

---

Quick Summary

Typical PTU workflow:

dmesg | grep ttyUSB
screen /dev/ttyUSB0 9600
TP-800

The camera should now be positioned correctly.