AD9951 Direct-Digital VFO, Parts List                                WA1FFL, J. Hagerty 

U1. Atmel AT89S8253-24PU microprocessor, supplied in parts kit.

U2. Analog Devices AD9951YSVZ Direct-Digital Synthesizer, supplied in parts kit (soldered on circuit board).

U3. Analog Devices AD8005ANZ, RF op amp. Supplied in parts kit.

U4, U5: National Semiconductor LM117H-ND, metal can package. U4 has a small heat sink (HS259-ND in Digi-Key catalog)

U6, U7. Texas Instruments TPS79118DBVR 1.8 volt surface-mount regulators, soldered on circuit board.

U8. Connor-Winfield, 5-volt clock oscillator, type AC52, 150 MHz.; supplied with parts kit.

U9. LM340AT-5.0, TO-220 regulator.

U10. 10Kohm, SIP (single-inline package) resistor pack,  # 770101103P. mfd. by CTS (available at Digi-Key).

Y1. 20 MHz microprocessor crystal,  Digi-Key part #CTX062-ND, HC-49 series.

T1. Mini-Circuits T1-1T-KK81 surface-mount transformer. This is a catalog item available on the Mini-Circuits web site. Small-quantity orders are welcome. The transformer is not hard to solder to the board; use a small tip size and avoid unnecessary heat.

R1. 1.5K, 1%     Note: All resistors are 1%, through-hole, ¼ watt, metal film.

R2. 240 ohms, 1%

R3. 392 ohms, 1%

R4. 240 ohms, 1%

R5. 3.85K, 1%

R6-R9, R14: 51 ohms, 1%

R10-R11, 33K, 1%

R12. 56.2 ohms, 1%

R13. 499 ohms, 1%

R15. 3.3K, 1%

R16. 1K, 1%

C1, C3,C10,C32: 0.1 uF., 50 v. ceramic (through-hole) capacitors

C2, C4,C7,C11,C37: 1.0 uF., 50v. ceramic (through-hole) capacitors

C8: 100 uF. tantalum, 15 volts rating or greater. Be careful of correct polarity. Note: This capacitor value is different than that given in the article and was increased to improve 5V transient response upon start-up. The “+” side is connected to pin 40 of the microprocessor.

C5, C6: Omit these for the Atmel microprocessor; it is meant to operate without them. (only Y1 is needed).

C9, C12-C21, C30: 0.1 uF., surface-mount capacitor (Note: All SMT capacitors are 1206 size).

C22-C27: Surface-mount capacitors, 1206-size. See Filter Table for component values, depending on the desired cutoff frequency and filter type (i.e., Chebyshev vs. Elliptic).

The 30 MHz Chebyshev is the simplest and is highly recommended. It gave me excellent spectral plots.

C29, C33: 0.01 uF. ceramic, 50 volts (through-hole)

C31, C39: 1.0 uF., surface-mount (1206 size)

C34, C36: 68 pf., 50 volts, ceramic (through-hole)

C35: 150 pf., 50 volts, ceramic (through-hole)

C38, C40: 0.01 uF., surface-mount (1206 size)

L1-L3: Surface-Mount Inductor, Coilcraft type 1008CS or equivalent.

See Filter Table for values. Note: check Mouser or Digi-Key for Toko, Murata, or similar substitute. Coilcraft has an excellent, easy-to-use sample request web site. For the Chebyshev filter, L1-L3 are identically = 330 nH.

L4, L5:  7 turns #22 enameled wire on T50-6 core (cores available from Amidon). Try requesting samples. The article shows 6 turns; 6-7 turns will work fine.

Miscellaneous Discretes:

D1. 1N5819  Schottky rectifier. (Note: Any diode or rectifier rated at 500 ma. or greater will suffice here). Another example is a 1N4001.

F1. Raychem RXEF025-ND electronic fuse, 250 ma. rating (available at Digi-Key).

The RXEF025-ND is the new lead-free version.

J1. BNC connector, 3-or 4-prong, pc mount. Supplied with parts kit while supplies last.

SW1, SW2, SW5, SW6: momentary tactile push-button switches, miniature type,

C&K model 8020, Jameco catalog.

SW3, SW4, SW7, also switches for CW/SSB and +/- offset lines (if they are not hard-wired): SPST miniature toggle switch.

Shaft Encoder: 5-volt logic levels;  Grayhill 61C11-01-08-02, Grayhill 25LB10-Q (mechanical version). For the mechanical encoder, see application note for connecting external resistors and capacitors. It is very easy and will save a significant amount of money.

Display: LCD Display, 2 rows x 16 columns: Optrex DMC-16202NY-LY-AZE-BJN.  

40-pin DIP (dual-inline package) socket, 0.6” spacing, machined type preferable (use as high a quality socket as possible), pc solder type. Supplied with parts kit.

TO-5 heat sink, Digi-Key part # HS259-ND.

Standoffs (optional). Use ½”-1” standoffs with # 4-40 machine screws and lock washers to hold them on. This will make the board easier to handle. Be careful not to touch the metal can regulator on the upper-right corner with the 4-40 screw.