When installing an aftermarket ECU sometimes you run out of inputs or outputs, to get around this you can use a CAN IO expander. There are a lot of different options on the market, each with their own features and use cases. The number of options can be overwhelming, so we’ve put together this article to help give an overview of each option to help you pick the right one for your project.
Most of the IO expanders on the market are fairly similar with a mix of analogue 0-5V inputs, digital switched inputs, and outputs. The options come in a number of form factors, from boards which need soldering to, to fully enclosed expanders with connectors for connectivity.
Before getting into the nitty gritty of each IO expander, we’re going to cover a few of the details about some of the input and output limitations which are mentioned.
Analog Inputs
Analog inputs are generally used for sensors and receive a 0-5V signal which corresponds to the sensor reading. A pressure sensor for example may have a range of 0-5 BAR, with the sensor reading 0.5V at 0 BAR and 4.5V at 5 BAR. This means that the ECU can use the voltage being input to determine a real world value from the sensor.
Depending on the sensor, a pullup resistor may need to be added, some IO expanders have these built in and others will require them to be wired in if needed.
Digital Inputs
Digital inputs are commonly used for simple on or off switches, and many of the IO expanders only have this type of functionality.
Some sensors, like ethanol sensors, and speed sensors use a digital input to deliver a more complex message. In the cases of ethanol sensors and speed sensors, the sensor outputs a signal in the form of a frequency. Some IO expanders don’t have the capability to read these frequency and can only be used for on-off functionality.
The other thing to consider is that some IO expanders can only take a 5V input on the Digital Inputs, this means that you cannot use 12V on these inputs. Depending on your use case this may be inconvenient as many vehicle circuits and switches will run on 12V and you may have to run a separate 5V line to your switch rather than reusing factory wiring.
Outputs
Outputs come in a few different forms with the most simple being an on or off output, some outputs are able to be pulsed and deliver an output a waveform with variable duty and frequency.
The other factor to consider is whether the output is capable of high side switching, or just does low side switching. Low side switching is the most commonly available and means that the device must have 12V already supplied, and the IO expander will connect the 12V to ground in order to power the circuit. High side switching is the same concept, but the IO expander can supply the 12V and the device only needs to be grounded in order for the IO expander to power the circuit.
Why might you use each output type?
An on or off style of output is great for switching on things like, mechanical relays, lights, O2 heaters, single speed fans, and more.
PWM outputs are widely used on vehicles and can be used to drive a solid state relay, thermofans, fuel pumps, boost control solenoids, VVT solenoids, and more.
While these types of outputs can be used for a lot of applications, the current limits on most IO expanders mean that the use cases are more limited, as solenoids, fans, pumps and motors often have a high current draw and would need a relay to be used with the IO expander anyway. In these cases depending on the PWM speed, a solid state relay may need to be used.
If using an IO expander to control a relay with low side switching, ensure that the relay trigger power has a separate ignition switched supply as many IO expanders and even ECUs switch the outputs to ground when power is off. If you use the battery power for the relay trigger as well as the supply for the high current device your relay can be switched on when the car is turned off.
Overview
PT Motorsport IO Nano
$69
Our first IO expander, the Nano is on it’s third revision. Offering a small form factor option, this was originally designed for use with steering wheel buttons, but proved to be a versatile offering, suitable for various uses especially in projects where space is a factor.
Inputs and Outputs:
4x 0-5V analog inputs. 0-5V only
4x On-off state ground switched digital Inputs
4x 200ma low side digital pulsed outputs (state or PWM only, with 490hz or 980hz as the PWM frequencies)
Connectivity:
4 pin JST for CAN and Power
5 Pin JST for DPOs and 12V
Size:
67.5×18.5x16mm
Can be reduced to 51×18.5x16mm with the end tabs removed.
PT Motorsport IO Mini
$125
The Mini is the Nano’s big brother, with a larger form factor, and connectors for each input and output. Due to the larger size, the Mini has a few extra features over the Nano, with built in pullup resistors and 12V input protection. With the step up comes the ability to read frequencies on one of the digital inputs.
Inputs and Outputs:
4x 0-5V analog inputs. 12V protection in place, but will only read values from 0-5V, and value over 5V will just show 5V. Built in 1K pullup resistors, which require soldering to activate.
4x On-off state ground switched digital Inputs. 12V protection in place. Digital input 1 able to receive frequencies.
4x 200ma low side digital pulsed outputs (state or PWM only, with 490hz or 980hz as the PWM frequencies)
Connectivity:
4 pin JST for CAN and Power
4 pin JST for DPOs
5 Pin JST for Digital inputs and GND
6 Pin JST for Analog inputs, 5V and GND
Size:
68x53x28mm
With the case removed, the board size is 46.5x40x15.5mm
CAN Checked – CFE18 (v2)
$159.89
The CAN Checked CFE18 is a small but powerful IO expander, with a total of 17 inputs and 3 outputs it allows for a large number of extra inputs in a very small form-factor.
Inputs and Outputs:
9x 0-5V analog inputs. 0-5V only. Built in 20K-50K pullup resistors, which use software to activate.
8x On-off state Digital Inputs
3x 500ma outputs (state only)
Connectivity:
Solder to board
Size:
29x27mm
ECU Master CAN Switch Board
$240
The ECU Master CAN Switchboard is another PCB style IO expander, with a total of 16 inputs and 4 outputs it allows for a large number of extra inputs and has the smallest overall form-factor on this list.
Inputs and Outputs:
8x 0-5V analog inputs. 12V protection in place, but will only read values from 0-5V, and value over 5V will just show 5V. Built in 1K pullup resistors, which use software to activate.
8x On-off state ground switched digital Inputs
4x 500ma low side outputs (resistive and inductive loads)
Connectivity:
Solder to board
Available with a connector in the PT Motorsport Connector PCB, which uses an AMP Superseal connector for all IO
Size:
25x25mm
61x81x33mm in the PT Motorsport Connector PCB
PT Motorsport IO DTM
$249
The IO DTM is the top of the line offering from PT Motorsport IO, with Deutsch DTM connectors for easy project integration it is the most advanced IO expander offered by PT Motorsport. With the highest current output handling on this list, it can directly power some lights and solenoids without needing an additional relay. The single frequency input is also great for adding either a flex sensor or a speed sensor to a project without having to juggle digital inputs on the ECU itself.
Inputs and Outputs:
4x 0-5V analog inputs. 12V protection in place, but will only read values from 0-5V, and value over 5V will just show 5V. Built in 1K pullup resistors, which require soldering to activate.
4x On-off state ground switched digital Inputs. 12V protection in place. Digital input 1 able to receive frequencies.
4x 3A digital pulsed outputs (state or PWM only, with 490hz or 980hz as the PWM frequencies). Limit of 7A total across all outputs.
Connectivity:
4 pin Deutsch DTM for CAN and Power
6 Pin Deutsch DTM for DPOs and 12V
12 Pin Deutsch DTM for Analog and Digital Inputs, 5V, and GND
Size:
107x30x51mm
CAN Checked – MCE18
$335
The MCE18 has the same functionality as the CFE18, but with an easy to mount case, and an AMP Superseal connector. This connector makes it quick and easy to change the pinout and add additional circuits when compared to soldering on the CFE18.
Inputs and Outputs:
9x 0-5V analog inputs. 0-5V only
8x On-off state Digital Inputs
3x 500ma outputs (state only)
Connectivity:
AMP Superseal connector for all IO
Size:
68x83x45.5mm
Haltech IO 12 Expander
$591
If you need to read additional Digital frequency inputs as well as PWM an output at a specific duty and frequency, the Haltech IO 12 is the expander to get.
Inputs and Outputs:
4x 0-5V analog inputs. With 1K selectable pullup resistors which use software to activate.
4x Digital Pulsed Inputs. 12V tolerant with the ability to read frequency signals.
4x 1A Digital Pulsed Outputs, with variable frequency and duty
Connectivity:
24 Pin Tyco connector for all IO
Size:
98x64x28mm