About the article

Serial transceiver

Electrically isolated RS232

Serial transceiver
This transceiver electrically isolates the TxD and RxD lines from the PC, provides an isolated power supply and also looks after the bi-directional conversion between TTL levels and symmetric RS232 levels.Frequently, a microcontroller system should or must have an electrically isolated connection to the RS232 interface of the PC. This can be necessary when the target system works at a completely different voltage level, or when earth loops must be avoided.The circuit described here can isolate potentials up to 2500 Veff or 3000 Vdc, depending on the type of optocoupler used. It uses only relatively easily obtained components, and it does not include any homemade inductors. Power for the circuit is provided by a mains adapter. A Maxim MAX232 interface driver is incorporated into the circuit to convert signals to the PC from TTL to RS232 levels (±12 V), and signals to the microcontroller system from RS232 to TTL levels.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1 = 100k?
R2,R5 = 470?
R3,R4 = 1k?
R6 = 680?
C1...C4 = 1µF 63V radial
C5,C7,C8,C10,C11,C12 = 100nF
C6,C9,C13 = 10µF 63V radial
D1 = LED, high efficiency
D2 = 1N4002
IC1,IC2 = 74HC00
IC3 = MAX232
IC4,IC5 = 6N137
IC6 = NMV0505SA (Newport, Farnell)
IC7 = 7805
K1 = 9-way sub-D socket, PCB mount, angled pins
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