Simulate a three-phase induction motor using the DigiKey motor simulator. It includes an LED ring to show the motor’s rotation direction (Video 1). It also includes an overload pushbutton that closes a dry relay contact. When combined with an external resistor (not included) the pushbutton will trigger an overload of the motor starter’s thermal overload block.
- Download the Part List/BOM (or the public MyList for easy ordering)
- Download the KiCad files
- Download the Gerber files
- Download the Microcontroller (MCU) code
Follow this link for additional information about motor starters.
Key Takeaways
-
Designed for classroom use with 24V PLCs and safety relays.
-
The LED ring indicates rotational direction when paired with a three-phase reversing motor starter.
-
A push button in the center of the PCB activates a relay to place a resistor across the incoming 24V, letting the user test their driver’s over-current protection.
-
An eight pin ATTiny MCU handles the LED animation.
-
Programming the ATTiny MCU can be done using any Arduino Uno as an ISP (hook up instructions are included at the beginning of the code)
-
The voltage direction is sensed with an opto-isolator/photo-coupler.
-
Through hole components were selected to make assembly as easy as possible.
-
Charlieplexing was utilized to drive 10 LEDs via 4 pins. (4 pins could drive up to 12)
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Teach It → Kits
Difficulty: 
Student — difficulty levels explained
Author: Brian German | Senior Technical Content Developer, DigiKey
Last update: 25 Mar 2026
Video 1: Video of the DigiKey’s motor simulator in operation. A large load resistor is shown in the background.
Designed for Education
The motor simulator was designed for the education environment.
-
The footprint matches the Phase Dock 10177 platform spacing. An example installation is shown as the Figure 1 PLC Trainer.
-
The simulator operates on 24 VDC. This allows students to focus on control logic in the lab environment without the exposure to high voltage AC mains voltage.
-
The LED rotation indicates polarity. Student may therefor simulate a motor connected to a motor starter such as Siemens 3RT2015 shown in Figure 2.
-
The simulator’s overload pushbutton connects the simulator to a user-supplied load resistor. The resistor is sized to trip the motor starter’s overload block. For example, a 12 Ω 50 W resistor is a good match for either the Siemens 3RU21160JB0 or the Schneider DPER06 thermal overload.
-
A single 24 VDC power supply can power both the PLC and the simulator. The power supply must supply enough current for both the user-supplied load resistance and the PLC. Continuing with the previous example, a power supply of 24 VDC at 3 A is recommended.
Figure 1: Image of the DigiKey PLC trainer featuring the motor simulator next to a S7-1200 PLC and a 3RT2015 motor starter.
Figure 2: Siemens 3RT2015 reversing motor starter with circuit breaker and thermal overload.
Circuit Design Highlights
I added the typical 2x6 header for any who had an AVR ICSP (in-circuit serial programming) device handy, as there was plenty of board space. I also added spots for 1x4 female headers next to the MCU for direct wire programming from an UNO – that also make it easy to probe its pins. I labeled the pins on both sides, so these female headers can be mounted to either side.
Aaron mentioned adding a ballast resistor (R3 here) to take some of the heat dissipation burden from the LDO, like a current limiting resistor for an LED. This had never crossed my mind in the past and it worked beautifully.
In the BOM, the part numbers for the blue and yellow tested LEDs are listed as well as their recommended resistors. These have a wide viewing angle and can be seen easily in a brightly lit room,
I was encouraged not to use charlieplexing but I had never had a worthy occasion to try it before and went for it. Thanks to some jive programming, I got it working- eventually. The requested aesthetic to the LED animation was to have it fade out after the leading LED went past. At first, the code given from ChatGPT kept thinking it was delivering that but it never did- just the leading LED alone. I changed the prompt many times to no avail, and then it hit me, ‘the AI might be trying to apply traditional fade-out code techniques, but this is charlieplexing’. I changed the prompt to apply 50% of the cycle time to the leading LED and the other 50% to the fading LED. Bingo! AI isn’t all knowing- yet.
The Mounting holes needed to be 50mm apart, square, to mount on the 25mm spaced grid, with 4.2mm holes for a #8 or an M4 screw for mounting via standoffs.
Tech Tip: LEDs with a wide dispersion angle were selected for this project…
Figure 2: Wire diagram showing how to connect the DigiKey motor simulator to a three-phase reversing motor starter.
Figure 3: Schematic of the DigiKey motor simulator.
Programming the Simulator
- Copy and paste the microcontroller (MCU) code into your Arduino Sketch.
- Connect the wires as listed in lines 6-11 of the code.
- Follow the Steps listed on lines 13-18.
Simulator Parts List
| Reference | Qty | Value | DKPN |
|---|---|---|---|
| C1 | 1 | CAP CER 1UF 25V X7R RADIAL | 445-173261-1-ND |
| C3 | 1 | CAP CER 2.2UF 50V X7R RADIAL | 445-173138-1-ND |
| D0 - D9 | 10 | A - B,A - C,A - D,B - A,B - C,B - D,C - A,C - B,D - A,D - B | 1830-1018-ND |
| D10 | 1 | BRIDGE RECT 1PHASE 160V 2A WOG | 4878-B80R-ND |
| D11 | 1 | TVS DIODE 25.6VWM 41.4V DO204AL | 13-P4KE30CA/BCT-ND |
| D12 | 1 | DIODE STANDARD 100V 200MA DO35 | 1N4148FS-ND |
| J1,J2 | 2 | TERM BLK 2POS SIDE ENTRY 5MM PCB | 1818-QT02ASB83H0000G-ND |
| J3 | 1 | CONN HEADER VERT 6POS 2.54MM | 2057-PH2-06-UA-ND |
| J4 | 1 | IC SOCKET, DIP, 8P 2.54MM PITCH | 2057-ICS-308-T-ND |
| J5,J6 | 1 | RECEPTACLE STRIP 4P 2.54MM PITCH | 2057-RS1-04-G-ND |
| K1 | 1 | RELAY GEN PURPOSE SPST 5A 24V | 2449-J1131AS24VDC.20-ND |
| R1 | 1 | RES 4.7K OHM 5% 1/4W AXIAL | CFM14JA4K70CT-ND |
| R2 | 1 | RES 1K OHM 5% 1/4W AXIAL | S1KQCT-ND |
| R3 | 1 | RES 1K OHM 1% 0.6W AXIAL | 13-MF0207FRE52-1KCT-ND |
| R4 - R7 | 4 | RES 240 OHM 5% 1/4W AXIAL | 738-CFM14JA240RCT-ND |
| SW1 | 1 | SWITCH PB SPST-NO 25MA 50V | 2449-NCA1-ND |
| U1 | 1 | OPTOISOLTR 5KV 1CH TRANS 4-PDIP | 488-FOD785C-ND |
| U2 | 1 | IC MCU 8BIT 8KB FLASH 8DIP | ATTINY85-20PU-ND |
| U3 | 1 | IC REG LINEAR 5V 150MA TO92 | AP7381-50V-ADICT-ND |