Kit Building Questions

We no longer sell kits but these questions relating to building a BitScope remain available here for those people wanting to build one using parts they supply themselves.

I'm missing some parts like the 150uh choke (L1) which is in the schematics but not shown on the photo included in the schematic package.

The photo is correct - replace the choke with a link.

Should I follow the silkscreen component values instead of the included schematics ?

Use the schematic, it is more up to date.

R53 on the silkscreen shows 5K7 resistor which is not a standard value.

The photo shows a 5K6 instead which is what you should use, 5K7 value is a typo.

The schematic and board silkscreen show 5 "OP-71" single channel op-amp's. (U14, U15, U16, U23, and U24) but the op-amp's included in the kit are: two TLC071C's, two AD8047's, and one AD8048. Which ones go where ?

Use the TLC071C for U23 and U24. They are JFET op-amps which are preferred for the inputs.

Use the AD8047 for U14 and U16. This is the same as BS200 scopes. These can be substituted with AD 8055AN if AD8047 is becomes hard to get.

Use the AD8048 for U15. It is a X5 version of the AD8047 or MAX477 and can also be substituted by an AD 8055AN.

Use the TLC072 (dual op-amps) for U25 and U28.

The TLC07x op-amps have limited bandwidth compared to BitScope's rated 100 MHz input bandwidth. Why do you use them ?

The BK300 kit is supplied with TLC071 and TLC072 OP-AMPs for the input stages (U23, U24 and U25) because these are the fastest DIP package J-FET OP-AMPs available. They are used as substitutes for the expensive and difficult to use but higher bandwidth SMT AD8085 and AD8086 modules used in BS300S.

J-FET OP-AMPs are preferred to eliminate small input offsets that can arise using bi-polar OP-AMPs but if higher bandwidth is more important than a small offset (around 100 mV) you can substitute bipolar equivalents MAX477 or AD8055/AD8056 which are 300 MHz devices.

Can I socket the op-amps and upgrade them later ?

Yes. Depending on demand, we may offer a 100MHz set of op-amps for U25, U23 and U24 (as used in our manufactured versions) as an upgrade. These SMT modules have AD 8065/8066 devices on them with decoupling and 24R feedback resistors (mounted on the underside). By putting the feedback on the SMT module, they are safe to socket. The -ve input pin of the module is not connected to the op-amp. These modules are the ones you see on the photo.

Can I socket the other ICs?

Yes - but use high quality sockets - machine pin if possible. Remember that sockets do increase the lead length and contribute to noise, but probably not a great deal. Most critical are the high speed op-amps - they can oscillate. When we designed the SMT modules, we put the critical feedback resistors on the pcb and disconnect the -ve input from the module pin. TLC071/2 op-amps will be stable in sockets as is.

I found a discrepancy between the schematic and the silkscreen on the PCB. For R63, the schematic says that this has a value of 4K7 and the silkscreen on the board says 10K. In the hi-res picture, it looks more like 10K but I just want to confirm the correct value for this resistor.

Not critical - but use 10K.

What setting should I use for the CLK jumper - 40MHz or 20MHz?

20MHz. At present all BS300 scopes use the 16F871 which runs at 20MHz. Later we may move to an 18F which can run at 40MHz. This will involve changing that jumper.

What do I need to know about soldering a 4 Layer PCB?

The BS300 PCB is a high quality multi layer PCB designed for wave soldering (or similar). To hand solder it, you need a good quality temperature controlled soldering station that can heat the joints to the correct temperature. Most pins will be straightforward. Be careful with GND or POWER pins that are connected to the inner layers. The copper will act as a heatsink and make soldering these joints more difficult.

Many Universities have small PCB mfg capabilites and may be able to help if you get into trouble. It may even be possible to run your board thru a wave solder machine to clean it up (after assembly). Apart from cosmetics, a correctly hand soldered PCB will perform as well as a production unit

Last modified: Tue Jun 8 14:33:40 EST 2010