# PIC16F628A DTMF Relay Audio Switch ## Description Rebuilt two-layer PIC16F628A DTMF relay audio switch with 12 V input, MT8870 decoding, PIC16F628A control, relay driver, and audio switching path. ## Project Details - **Owner:** frzt - **Created:** 4/1/2026 - **Last Updated:** 4/1/2026 - **Visibility:** Public - **System Architecture:** ```mermaid flowchart TD PWR[12V Input and 5V Regulation] --> DTMF[MT8870 DTMF Decoder] DTMF --> MCU[PIC16F628A Control Logic] MCU --> DRV[Transistor Relay Driver] DRV --> RELAY[SPDT Audio Relay] AFIN[AF_IN] --> DTMF AFIN --> RELAY RELAY --> AFOUT[AF_RELAY_OUT] CTCSS[CTCSS Input] --> MCU ICSP[ICSP Header] --> MCU ``` - **Forks:** 1 ## Key Components ### D1 — [1N4007RLG](https://www.flux.ai/jecstronic/1n4007rlg~07j.md) - Manufacturer Name: onsemi - Manufacturer Part Number: 1N4007RLG - Datasheet URL: https://www.onsemi.com/pdf/datasheet/1n4001-d.pdf - License: https://creativecommons.org/licenses/by/4.0/ - Package: DO-41 - Role: Input Protection - Role Details: Reverse polarity / series protection diode on +12V input - Part Type: Diode **Pins:** - anode [pin 2] - cathode [pin 1] ### D2 — [1N4007RLG](https://www.flux.ai/jecstronic/1n4007rlg~07j.md) - License: https://creativecommons.org/licenses/by/4.0/ - Package: DO-41 - Part Type: Diode - Role Details: Relay coil flyback suppression diode - Manufacturer Name: onsemi - Manufacturer Part Number: 1N4007RLG - Role: Flyback Diode - Datasheet URL: https://www.onsemi.com/pdf/datasheet/1n4001-d.pdf **Pins:** - anode [pin 2] - cathode [pin 1] ### J1 — [691137710002](https://www.flux.ai/adrian95/691137710002~c39.md) - Role: 12V Input - Manufacturer Name: Würth Elektronik - Part Type: Connector - License: https://creativecommons.org/licenses/by/4.0/ - Package: THT - Manufacturer Part Number: 691137710002 - Datasheet URL: https://www.we-online.com/katalog/datasheet/691137710002.pdf - Role Details: +12V_IN and GND supply connector **Pins:** - 1 [pin 1] - 2 [pin 2] ### J2 — [2-644861-2](https://www.flux.ai/adrian95/2-644861-2~vfq.md) - License: https://creativecommons.org/licenses/by/4.0/ - Role: AF Input Connector - Role Details: AF_IN and GND external audio input - Manufacturer Name: TE Connectivity AMP Connectors - Package: THT - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=644861&DocType=Customer+Drawing&DocLang=English&PartCntxt=2-644861-2&DocFormat=pdf - Part Type: Connector - Manufacturer Part Number: 2-644861-2 **Pins:** - Pin_1 [pin 1] - Pin_2 [pin 2] ### J3 — [2-644861-2](https://www.flux.ai/adrian95/2-644861-2~vfq.md) - Package: THT - License: https://creativecommons.org/licenses/by/4.0/ - Role Details: AMP_IN and GND connection to downstream amplifier - Manufacturer Name: TE Connectivity AMP Connectors - Role: Amplifier Connector - Manufacturer Part Number: 2-644861-2 - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=644861&DocType=Customer+Drawing&DocLang=English&PartCntxt=2-644861-2&DocFormat=pdf - Part Type: Connector **Pins:** - Pin_1 [pin 1] - Pin_2 [pin 2] ### J4 — [2-644861-2](https://www.flux.ai/adrian95/2-644861-2~vfq.md) - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=644861&DocType=Customer+Drawing&DocLang=English&PartCntxt=2-644861-2&DocFormat=pdf - Part Type: Connector - Manufacturer Part Number: 2-644861-2 - Package: THT - Role: CTCSS Connector - Manufacturer Name: TE Connectivity AMP Connectors - Role Details: CTCSS_IN and GND external input - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - Pin_1 [pin 1] - Pin_2 [pin 2] ### J5 — [87224-5](https://www.flux.ai/adrian95/87224-5~c5b.md) - Manufacturer Name: TE Connectivity - Manufacturer Part Number: 87224-5 - Role: ICSP Header - Role Details: 1x5 PIC ICSP programming connector - Part Type: Connector - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.arrow.com/en/products/87224-5/te-connectivity - Package: THT - Package or Case Code: HDRV5W66P0X254_1X5_1229X254X1074P **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] ### Q3 — [BC33740TA](https://www.flux.ai/adrian95/bc33740ta~5dt.md) - Manufacturer Part Number: BC33740TA - Part Type: Transistor - Package: TO-92-3 - Role: Relay Driver - Manufacturer Name: onsemi - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.verical.com/datasheet/on-semiconductor-bjt---general-purpose-BC33740TA-4544246.pdf - Role Details: NPN transistor driving 12V SPDT relay coil **Pins:** - B [pin 2] - C [pin 1] - E [pin 3] ### RL1 — [JS1-12V-F](https://www.flux.ai/lcsc/js1-12v-f~kei4.md) - Manufacturer Name: PANASONIC(松下) - Package: THT - Manufacturer Part Number: JS1-12V-F - Role Details: SPDT relay switching AF path between AF_IN and amplifier output path - Role: Signal Relay - Package or Case Code: RELAY-TH_JS1-12V-F - JLCPCB Part Class: Extended Part - LCSC Part Number: C498189 - Part Type: Power Relays **Pins:** - COIL1 [pin 5] - COIL2 [pin 2] - MAIN [pin 1] - NC [pin 4] - NO [pin 3] ### U1 — [PIC16F628A-I/P](https://www.flux.ai/adrian95/pic16f628a-ip~42t.md) - Manufacturer Part Number: PIC16F628A-I/P - Role: Microcontroller - Role Details: PIC16F628A main controller for relay-switched audio path - Manufacturer Name: Microchip Technology - Part Type: Microcontroller - License: https://creativecommons.org/licenses/by/4.0/ - Package: PDIP-18 - Datasheet URL: https://ww1.microchip.com/downloads/en/DeviceDoc/40044G.pdf **Pins:** - RA0/AN0 [pin 17] - RA1/AN1 [pin 18] - RA2/AN2/VREF [pin 1] - RA3/AN3/CMP1 [pin 2] - RA4/T0CKI/CMP2 [pin 3] - RA5/~MCLR/VPP [pin 4] - RA6/OSC2/CLKOUT [pin 15] - RA7/OSC1/CLKIN [pin 16] - RB0/INT [pin 6] - RB1/RX/DT [pin 7] - RB2/TX/CK [pin 8] - RB3/CCP1 [pin 9] - RB4/PGM [pin 10] - RB5 [pin 11] - RB6/T1OSO/T1CKI/PGC [pin 12] - RB7/T1OSI/PGD [pin 13] - VDD [pin 14] - VSS [pin 5] ### U2 — [MT8870DS1](https://www.flux.ai/lcsc/mt8870ds1~ogvm.md) - Manufacturer Part Number: MT8870DS1 - Role: DTMF Decoder - Part Type: Interface - Telecommunications - Role Details: MT8870-family decoder preserving Q1-Q4, StD, oscillator, and analog front-end behavior - Package or Case Code: SOIC-18_L11.6-W7.5-P1.27-LS10.3-BL - Package: DIP-18 - Manufacturer Name: MICROCHIP(美国微芯) - JLCPCB Part Class: Extended Part - LCSC Part Number: C1522188 **Pins:** - ESt [pin 16] - GS [pin 3] - IN [pin 2] - IN+ [pin 1] - INH [pin 5] - OSC1 [pin 7] - OSC2 [pin 8] - PWDN [pin 6] - Q1 [pin 11] - Q2 [pin 12] - Q3 [pin 13] - Q4 [pin 14] - St/GT [pin 17] - StD [pin 15] - TOE [pin 10] - VDD [pin 18] - VRef [pin 4] - VSS [pin 9] ### U3 — [LM7805CT/NOPB](https://www.flux.ai/adrian95/lm7805ctnopb~wo3.md) - License: https://creativecommons.org/licenses/by/4.0/ - Role: 5V Regulator - Manufacturer Part Number: LM7805CT/NOPB - Manufacturer Name: Texas Instruments - Part Type: Integrated Circuit - Package: TO-220-3 - Role Details: 7805 linear regulator from +12V_RAW to +5V - Datasheet URL: https://www.ti.com/lit/ds/symlink/lm340.pdf **Pins:** - GND [pin 2] - VI [pin 1] - VO [pin 3] ### VR1 — [3386P-1-103LF](https://www.flux.ai/adrian95/3386p-1-103lf~2jg.md) - Manufacturer Part Number: 3386P-1-103LF - Datasheet URL: https://www.bourns.com/docs/Product-Datasheets/3386.pdf - Manufacturer Name: Bourns Inc. - Package: THT - License: https://creativecommons.org/licenses/by/4.0/ - Role Details: 10k trimmer setting audio level into MT8870 input - Part Type: Potentiometer - Role: AF Level Adjust **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/frzt/pic16f628a-dtmf-relay-audio-switch~ly](https://www.flux.ai/frzt/pic16f628a-dtmf-relay-audio-switch~ly).* --- *Generated from [https://www.flux.ai/frzt/pic16f628a-dtmf-relay-audio-switch~ly](https://www.flux.ai/frzt/pic16f628a-dtmf-relay-audio-switch~ly)*