YADRO: Building the DRO:int4 kit

DRO:int4 Building the Kit

The construction is as robust as possible (short circuit protections) and most easy to assemble (low parts count).

All boards come with solder stop mask, placement screening and are fully electrically tested at the factory.

Sections:

Tools needed
populating the board
the first test

Because most people fear to build SMD-kits, the decision to build a conventional circuit was clear. This also reduces the skills and tools needed.

A good soldering iron (15…30 Watts),
some fine pliers to cut the wires,
a multimeter (advisable)
and some solder (I prefer 0.8mm diameter)

Populating the board:

First some advice about ESD is necessary:
The chips used in the interface are sensitive to electric discharge. That is the reason why the chips come on some conductive foam or in a protective container. Leave the chips there until it is time to solder them in. Discharge yourself by touching a radiator or some metal connected to earth. Do not wear clothes that tend to produce electrical charge (like synthetic fabric).

Those who know how to poulate a PCB won't go on reading. They do it the way they did many times before. Start with the low profile parts and work their way up. They will only start testing when they are finished. For those not so familiar, I have described a way that enables early testing.

Part#	Spec.
Capacitors
C1…C5, C10, C12, C13, C15	100n
C8, C9	22p
C6	10µ
C11, C16	1000µ
C7	22µ
C14	1µ
Resistors
R1, R2, R5…R12	100
R3	56
R4	220
R14, R15, 23	330
R16, R19..R22	3k9
R13, R17, R18	10k
Diodes
B1	B40C800
LED1	--
Integrated Circuits
IC1	MAX232N (TI) or MAX232ACPE (Maxim)
IC2	LM317LZ
IC3, IC4	LM2901N
IC5	CD4051N
IC6	Atmel ATtiny2313-20P
IC7	uA78S05
OK1, OK2	HCPL4502 or 6N136
Misc
Q1	20MHz X-tal
DC1	5V/5V DC/DC
J1	MTA02-100
J2	MTA03-100
X2	9 pin D-sub male
SV2…SV5	6 pin header
SV1	10 pin DIL-header, male
not drawn	power supply 7 … 9V AC, 200mA min.
not drawn	null-modem (x-over) cable 9 pin female/female

The PCB is double sided with the holes trough-contacted. So soldering is only done on the bottom side.

Parts that are oriented (polarized) have a red background color in the partial BOMs following.

Step 1

We start by soldering in the resistors on the main part of the circuit. Refer to the BOM and the screening on the PCB to put the right resistors in the right place. Cut the wires that about 1mm is protruding from the bottom side.

Part#	Spec.
R1, R2, R5…R12	100
R3	56
R4	220
R14, R23	330
R19..R22	3k9
R13, R17, R18	10k

Step 2

Electrolythic capacitors (C11, C16, C7 and C14) have a marking that is either "-" or "+". Be shure to match the + on the part with the + on the PCB.
B1 (bridge rectifier) has the orientation printed on. Not all bridge rectifiers do have the flat printed on the PCB. Levae a gap of about 5mm between PCB and the reftifier case to improve cooling.
IC2 and IC7's orientation can be seen on the photo or the PCB. LED1 has one (of the two) wires that is shorter. This shorter leg goes into the lower hole (near R23).

Part#	Spec.
C13, C15	100n
C11, C16	1000µ
C7	22µ
C14	1µ
B1	B40C800
IC2	LM317LZ
IC7	uA78S05
LED1

Step 3

By connecting the power connector to the PCB, we are ready for a first test: Depending on the kit you got, J1 is either a connector, or you use two wires. Orientation is not critical, as it is AC.

By applying power to the board, the LED should light up (if not, chances are that it was soldered in the wrong way round). You can now check the voltages V1:1 … V1:28. For a quick check, it is enough to test V1:1, V1:20, V1:23 and V1:26. See the plan for location of test points.

Step 4

We finish the power supply of the serial communications part and solder in the remaining resistors. The DC/DC-converter(DC1) has a dot on it's case. Match it with the dot on the PCB.

Part#	Spec.
Capacitors
C5	100n
C6	10µ
R15	330
R16	3k9
DC1	5V/5V DC/DC

You can now check the voltages on V2:1 … V2:3. Also check that the resistance between Ref1 and Ref2 is infinite (no connection).

Step 5

We continue by soldering in the remaining capacitors and the X-tal. Pay attention to use the propper (22pF) capacitors for C8 and C9.

Part#	Spec.
Capacitors
C1…C4, C10, C12	100n
C8, C9	22p
Q1	20MHz X-tal

Step 6

Next are the remaining connectors. If you don't have a connector for J2 (as on the photo), you might connect these cables at the very end.
If you have a connector for J2, the tang is pointing outwards of the board (see screening of the board).
Pin 6 of every SV2 … SV5 has to be cut off.

Part#	Spec.
J2	MTA03-100
SV2…SV5	6 pin header
SV1	10 pin DIL-header, male

Step 7

Nearing compleation, the ICs get at their place. Pay attention to be earthed. Pay attention to the parts orientation. ICs do have a notch or a dot in their case that has to match the printed notch on the PCB. Especially OK1 and OK2, despite sitting side by side, have different orientation. They are sitting back to back. :-)

Part#	Spec.
IC1	MAX232N (TI) or MAX232ACPE (Maxim)
IC3, IC4	LM2901N
IC5	CD4051N
IC6	Atmel ATtiny2313-20P
OK1, OK2	HCPL4502 or 6N136

Step 8

If you have no cable set, it is now time to finish the kit by connecting the serial connector. J2 has 3 solder pads (1 to 3). Pad 1 is marked with a "1" that goes to pin 2 of a 9 pin D-sub (male) connector J2:2 goes to pin 3 and J2:3 goes to pin 5 (ground) of the D-sub.

Before connecting the scales, you should double check the voltages at V1:9, V1:13, V1:16 and V1:20. It should be 1.55V (+/- 0.1V)