Perimeter Detect Circuit Examples


ZYMKEY and HSM security modules feature two independent perimeter circuits that can be configured to detect physical tamper intrusion events.

HSM Perimeter Detect|690x484

Electrical Requirements

Each perimeter loop should be connected with a 30 AWG wire or thicker and nominal length of 2 feet. For longer lengths contact Zymbit. The wire should be electrically insulated for all applications. A shielded cable may be necessary for electrically noisy or industrial applications.

Physical Circuit Connections

How these circuits are configured physically will vary depending upon the specific application, enclosure and security needs. Standard wires, custom flex PCBs and rigid PCBs may all be used to complete a perimeter loop circuit.

Here we share some practical examples of how to configure perimeter detect circuits for different applications and equipment.

To learn about software configuration and use of perimeter detect functions Learn more>


Direct Connect to HSM4 Hat

HSM4 HAT provides four pin header and FPC connectors to interface to perimeter circuits 1 and 2. This is convenient for rapid prototyping and small scale production situations. For high volume applications, different connector types are available - contact zymbit for more details.

Perimeter HDR (Header) Pinout

HSM4 HAT Perim Pinout HDR|582x500, 75%

Perimeter FPC (Flexible Printed Circuit) Pinout

HSM4 HAT Perim Pinout FPC|612x500, 75%

HSM Direct Connector - Hirose Header DF40HC(3.5)-30DS-0.4V(51)

HSM4 Module Pinout|690x435, 75%

Direct Cable Connect to Zymkey 4i

Perimeter circuits on Zymbit 4i are accessed from a standard microUSB connector.


Use a standard microUSB extension cable to close circuits P1 and P2 as follows.


Adapter Connect to Zymkey 4i

Several adapters are available from Zymbit that simplify connection from the microUSB to header and FPC. These are convenient for development. Buy Adapters >

Perimeter Adapter Types 2020.06|690x491

Flexible Security Shield Wrapping RPi4

HSM4 Security Module, fitted to PiHat1. Flex circuit connects to FPC connector on HAT

Security Blanket Wrapping Pi4_|600x427

Security Blanket Fitted to Pi4_1|690x353

Rigid Security Shield installed on ProtoKit4

A printed circuit shield is fitted into the lid of the ProtoKit 4 and pogo pins connect the top mesh to the the bottom board. When the lid is closed, the circuit is closed.

PerimShield Graphic 1|689x436

Zymit ProtoKit4-with-shield|690x460


Perim Shield Graphic 3|690x287

The shield connects the following four perimeter signals available on the protoboard:

  • PERIM_1B
  • PERIM_2B
  • PERIM_2A
  • PERIM_1A

ProtoKit4 Perim Circuits|690x404

FlexCable Wrap with PiZero Hat

Zymbit Tamper Circuit Example 20|375x500

Zymbit Tamper Circuit Example 21|375x500

Zymbit Tamper Circuit Example 22|375x500

SDCard Blocking Perimeter Adapter with PiZero Hat


Tamper Switches & FlexCable with Secure Compute Device

Zymbit secure compute motherboard for RPi

Zymbit Tamper-Circuit-Example-10|657x500

Zymbit Tamper-Circuit-Example-11|657x500

Zymbit Tamper-Circuit-Example-12|666x500

Zymbit Tamper-Circuit-Example-13|666x500

Internal Tamper Switches


Secure Compute Device in 2U Rack with External Tamper Switches