Abstract: In its simplest form, the PC voltmeter consists of a 4-channel, 10-bit A/D converter (IC2) with a few passive components, connected to the PC printer port via a 25-pin male D-type connector. In its simplest form, the PC voltmeter of Figure 1 consists of section "A" alone: a 4-channel, 10-bit A/D converter (IC2) with a few passive components, connected to the PC printer port via a 25-pin male D-type connector. Power is derived from pins 2 and 3, and the circuit draws about 1mA. Figure 1. This circuit and the associated Q-BASIC listing enable a PC to monitor and measure the voltages on four input channels. IC2's wide power-supply range (2.7V to 5.25V) allows operation from a variety of PC printer ports. The voltage at pins 2 and 3 is about 5V for a lot of desktop machines, but for portables it is more likely to be around 3V. IC2 handles them all. R10-R11 and C7-C8 filter the PC noise from this supply line. C6 and C9 decouple the 2.5V reference internal to IC2. To maintain 10-bit accuracy, the source impedances driving the ADC inputs (pins 2-5) must be less than 3kΩ. If not, you can buffer these inputs by adding the "B" section to the circuit. This quad op amp (configured as four noninverting buffers) has rail-to-rail inputs and outputs, operates with supply voltages down to 2.7V, and draws about 25µA per amplifier. To provide high-voltage protection, the op amps' very low bias current (1pA typical) allows 180kΩ resistors in series with each input without introducing excessive error (R1-R4 in section "C"). For additional (anti-aliasing) filtering you can add capacitors C1-C4, and to increase the full-scale range from 2.5V to 25V you can add R5-R8. Other variations: You can substitute a 12-bit MAX1246 for IC2 in place of the 10-bit MAX1248, but for 12-bit accuracy you must restrict the supply voltage to the range 2.7V to 3.6V. Alternatively, you can substitute a 12-bit MAX1247 and add an external reference such as the MAX872, which gives a 2.5V output for input voltages down to 2.7V. Two Q-BASIC listings are available, each written for the 12-bit circuit options. Listing 1 scans the four channels and displays each input voltage on the screen. Listing 2 displays the channel voltages, plots them vs. time on the screen, and lets you save the data to disk. 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 1988: Apr 10, 2003 MAX1248 16핀 QSOP 패키지로 제공되는 +2.7V ~ +5.25V, 저전력, 4채널, 직렬 10비트 ADC 전체 데이터 시트 (PDF, 256kB) 무료 샘플 MAX4164 SOT23, 마이크로파워, 단일 전원, Rail-to-Rail I/O Op 앰프 전체 데이터 시트 (PDF, 400kB) 무료 샘플   다운로드, PDF 형식 (38kB)  AN1988, AN 1988, APP1988, Appnote1988, Appnote 1988