Secure thermal print head
Methods and apparatus to detect if an authorized thermal print head (TPH) has been installed in a specific model or manufacturer printer are provided. The method provides a system to check the resistivity or impedance value at the TPH side, either upon printer boot-up or during printing operation. During printing operation, the impedance measurement may be executed for a time period at a fixed periodicity and/or one or more events. Based on the impedance measurement, the printer may determine that the impedance value matches the authorized TPH range value. In a case of non-matching impedance values or change of impedance values, the printer may prevent printing operation until an authorized TPH is installed.
1. A printer, comprising:
a thermal print head;
an authentication encryption integrated circuit (IC) associated with the thermal print head; and
an impedance control system, coupled to the thermal print head and authentication encryption integrated circuit (IC), configured to measure an impedance of one or more points of the thermal print head and the authentication encryption integrated circuit (IC),
wherein, based on the measured impedance, measured at start-up and measured over a time period, the impedance control system determines whether the thermal print head is authorized or not,
wherein, at start-up, if the measured impedance is equal to a predetermined value, the thermal print head is authorized; and
wherein, at start-up, if the measured impedance is not equal to the predetermined value, and if an impedance measurement condition is not completed, the impedance control system repeats the impedance measurement but if the impedance measurement condition is completed, the thermal print head is not authorized and the impedance control system prevents a printing operation.
2. The printer according to claim 1 ,
wherein, if variations of the measured impedance over the time period exceed a threshold, then the thermal print head is not authorized.
3. The printer according to claim 1 ,
wherein, the impedance control system measures the impedance at a fixed periodicity and/or one or more events.
4. The printer according to claim 1 ,
wherein, the one or more points of the thermal print head comprises thermal printer head power (VCC), authentication IC data line, and thermal print head data lines.
5. A printer, comprising:
a thermal print head;
an authentication encryption integrated circuit (IC) associated with the thermal print head; and
an impedance control system, coupled to the thermal print head and authentication encryption integrated circuit (IC), configured to measure an impedance of one or more points of the thermal print head and the authentication encryption integrated circuit (IC),
wherein, based on the measured impedance, measured at start-up and measured over a time period, the impedance control system determines whether the thermal print head is authorized or not,
wherein, at start-up, if the measured impedance is equal to a predetermined value, the thermal print head is authorized;
wherein, if a first impedance of internal circuitry for the authentication encryption integrated circuit (IC) is R and a second impedance of internal circuitry for one of the one or more points of the thermal print head is R, and the first internal circuitry and second internal circuitry are coupled in parallel, then the predetermined value is R/2±a margin, and
wherein, if the measured impedance is not R/2±a margin, then the thermal print head is not authorized and the impedance control system prevents a printing operation.
6. The printer according to claim 5 ,
wherein, if variations of the measured impedance over the time period exceed a threshold, then the thermal print head is not authorized.
7. The printer according to claim 5 ,
wherein, the impedance control system measures the impedance at a fixed periodicity and/or one or more events.
8. The printer according to claim 5 ,
wherein, the one or more points of the thermal print head comprises thermal printer head power (VCC), authentication IC data line, and thermal print head data lines.
9. A printer, comprising:
a thermal print head;
an authentication encryption integrated circuit (IC) associated with the thermal print head; and
an impedance control system, coupled to the thermal print head and authentication encryption integrated circuit (IC), configured to measure an impedance of one or more points of the thermal print head and the authentication encryption integrated circuit (IC),
wherein, based on the measured impedance, measured at start-up and measured over a time period, the impedance control system determines whether the thermal print head is authorized or not,
wherein, if the impedance measurement is not completed, the impedance control system repeats the impedance measurement, and
wherein, if the impedance control system determines the thermal print head is not authorized, the impedance control system then prevents a printing operation.
10. The printer according to claim 9 ,
wherein, at start-up, if the measured impedance is equal to a predetermined value, the thermal print head is authorized.
11. The printer according to claim 9 ,
wherein, at start-up, if the measured impedance is not equal to the predetermined value, and if an impedance measurement condition is completed, the thermal print head is not authorized and the impedance control system prevents the printing operation.
12. The printer according to claim 9 ,
wherein, if variations of the measured impedance over the time period exceed a threshold, then the thermal print head is not authorized.
13. The printer according to claim 9 ,
wherein, the impedance control system measures the impedance at a fixed periodicity and/or one or more events.
14. The printer according to claim 9 ,
wherein, the one or more points of the thermal print head comprises thermal printer head power (VCC), authentication IC data line, and thermal print head data lines.