True RMS Digital Voltmeter
with frequency counter
Materials
Gerber file
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Extra info / Update
Main Characteristics
- Four measurement ranges: 0.1 V, 1 V, 10 V, 100 V
- Voltmeter bandwidth: 20 Hz to 1 MHz (basic accuracy ±1.0 % of full scale)
- Frequency counter bandwidth: 1 Hz to 10 MHz (typ.), 25 MHz (max.) (±timebase error)
- Minimum input voltage for counter: approximately 50 mVRMS
- Input impedance: = 1 MO || = 50 pF
- Counter timebase: 100 ms, 1 s
- Adjustable trigger level: approximately ±0.15 V
- Autoranging (may be disabled)
- Offset correction and calibration facility
- Automatic scaling of frequency display
- Voltage displayed as RMS value or peak-to-peak value (for sinusoidal input)
- Crest factor: =4
- Two measurement inputs
Component list
Measurement Amplifier
Resistors
R1,R2, R5 = 47Ohm (SMD 0805)
R3,R4 = 27Ohm (SMD 0805)
R6 = 100k
R7 = 10k (SMD 0805)
R8 = 470kO (SMD 0805)
R9 = 900kO 0.1%
R10,R11 = 4kO7
R12 = 90kO 0.1%
R13 = 9kO 0.1%
R14 = 1kO 0.1%
R15 = 430Ohm (SMD 0805)
R16 = 430Ohm (SMD 1206)
R17 = 4kO7 (SMD 0805)
R18 = 4kO7 (SMD 0805)
P1 = 10kO (Alps type 290061)
Capacitors
C1,C2,C11,C13,C16,C19 = 100nF (SMD 0805)
C3,C4,C10,C12 = 4µF7 10V (293D/A)
C5,C6 = 10nF (SMD 0805)
C7 = 27pF (SMD 0805)
C8 = 10nF
C9 = 1nF (SMD 0805)
C14 = 1µF 10V (SMD 0805)
C15 = 10µF 10V (SMD 0805)
C17,C18 = 10µF 10V (293D/A)
C20,C21 = 2.5-35pF trimmer (C-TRIMM808-7.5)
C22 = 2nF2
C23 = 22nF
C24,C25 = 220pF
Semiconductors
IC1= ADA4862-3 (SMD)
IC3 = LTC1968CMS8 (MSOP-8)
IC4 = LT1016CS8 (SO-8)
D1,D2 = BAS45 (1N4148)
D3,D4 = BZW55-2.7 (SMD)
T1 = Dual FET PMBFJ620 (NXP)
Miscellaneous
Re1–Re4 = SIL7271-L 5V or MEDER SIL05-IA72-7ID
K1,K2,K3 = 2-way pinheader
K4,K5 = 4-way pinheader
2x SMA case socket
Metal case e.g. TEKO # 372
BNC case socket
Miniature rocker switch
7x 1nF feedthrough capacitor
PCB # 080331-1, see www.elektor.com/shop
Display board
Resistors
R3,R5 = 10kO (SMD 0603)
R4 = 10k
R6 = 33k (SMD 0603)
R7 = 4kO7 (SMD 0603)
R8 = 100kO (SMD 0603)
R11,R12,R13,R14 = 1kO (SMD 0805)
R15 = 1kO (SMD 0603)
Capacitors
C2,C4 = 1µF 10V (SMD 0603)
C3,C6,C7 = 100nF (SMD 0603)
C5 = 4µF7 10V (SMD 0603)
C8 = 18pF (SMD 0603)
C9 = 27pF (SMD 0603)
C10= 20pF trimmer (C-TRIMMCTZ3)
Semiconductors
IC1 = R8C13 (R5F21134FP, LQFP32) IC2 = LTC2420CS8 (SO-8)
IC3 = LT1790ACS6-2.048 (SOT23-6)
D1..D4 = 1N4148 (SOD-323)
T1 = BC558C (SOT-23)
T2–T6 = 2N7002 (SOT-23)
LED1–LED4 = LED, green (SMD 1206)
LED5 = LED, 3mm
Miscellaneous
LCD1 = LCD 2×16
JP1 = 2-way pinheader and jumper
K1,K2,K3 = 2-way pinheader
K4,K5 = 4-way pinheader
X1 = 20MHz quartz crystal, HC-49US12SMD
S1-S4 = pushbutton (Schurter # 1241.1614)
S5 = pushbutton (6mm)
PCB # 080331-2, see www.elektor.com/shop
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