IMSAI 8080

Some pictures documenting the restoration of an IMSAI 8080

After removal and cleaning of the front panel. Everything looks in very good condition although some of those capacitors might need replacing after 38 years

After complete disassembly, the reconstruction can begin. Replacement motherboard screws were needed due to the age (3/4" 6-32 nylon with 6-32 1/4" alu spacers)

The famous 'Big Z' card compete with monitor EPROM

Brand new Jade 'The Memory Bank' card

+8v and +/-16v supplies all working within tolerance

Replacement of the front panel (CP-A)

Powered up and running the Big Z monitor program

The Big Z card and The Memory Bank

piRadio - Desktop Receiver

Differs little from the portable model aside from the additional LNA, speaker and audio amplifier

The LNA is the gold colour PCB on the right

piRadio Hardware & Connections

Hardware

The connections detailed here work with the code uploaded to Github however it is a simple enough procedure to reconfigure as needed. Most of the hardware connections are defined in oeta.h

1x case

1x rPi (either Model A or B works fine, Model A uses less power so for portable operation it might be a better choice. a WiFi USB dongle can be used for network mode at home)

1x RF upconverter. I chose the Ham-It-Up because it has a switch for passthrough or up convert mode. If you choose an up converter without this feature you'll need to set up a way to disable it if you want to receive above HF) 

1x DVB-T dongle (E4000 are the best models with the widest receive band)

1x SMA male coax cable, 6" (one end will be cut so male-male or male-female are fine)

1x 2.2" SPI LCD (ebay is a good source, ~$8)

1x 3.5mm panel moult headphone socket (stereo or mono is fine depending on preference)

Push button rotary encoder with 6mm shaft and knob

2x SPDT

1x DPDT

1x MausBerry shutdown circuit that allows use of your own switch (if you want keyboard-les operation). This seems the simplest approach or you can create your own using a small Arduino board. If you aren't running on battery then this isn't really needed

4x PCB board spacers, 15mm, (brass or plastic are ok)

4x 40mm PCB spacers to separate the acrylic sheets

2x acrylic sheets (A5 size)

A selection of duPont cables for connecting to the rPi

1x USB type B male socket

Connections

P1-4: To Ham-It-Up converter 5v

P1-6: To Ham-It-Up converter GND

P1-14: Rotary Encoder (middle pin)

P1-16: Rotary Encoder (right pin with pins facing away)

P1-18: Rotary Encoder (left pin with pins facing away)

P1-20: LCD GND & Menu select (push button on the rotary encoder) (splice cable)

P1-22: LCD D/C

P1-24: LCD CS

P1-1: LCD 3.3v

P1-3: Menu select (push button on the rotary encoder)

P1-5: TCP / Standalone radio mode select switch

P1-7: Mausberry switch out

P1-9: Menu select (push button on the rotary encoder)

P1-11: Mausberry switch in

P1-13: HF / passthrough mode switch

P1-15: LCD reset

P1-19: LCD SDI

P1-21: LCD SDO

P1-23: LCD SCK

P1-25: TCP / Standalone radio mode select switch

The code has been posted to Github as a fork of rtl_sdr: https://github.com/LomTuby/rtl-sdr

DVB-T receiver (E4000)

Upconverter

Rear view

piRadio Portable - piRadio2

After a lot of development, I've finally completed the portable piRadio, an RTL8192-based SDR radio that runs either as a server or in standalone mode.

In server mode it behaves as one would expect, running rtl_tcp streaming data packets over the network. The on-board LCD display will indicate the assigned IP address making for simple connections from your PC-based software such as GQRX (OSX) or HD SDR etc. The switch on the right can be used to select the mode and it is read at boot up.

In standalone mode, the software running natively on the Raspberry Pi displays a realtime spectrum scope. In addition, when the rotary control  is pushed, a menu is displayed allowing one to choose the modulation mode, the step size and the gain.

The software is based on rtl_fm and kiss_fft and highly optimized to run on the Raspberry Pi's limited resources. The kernel is customized to support SPI LCDs.

The hardware also includes the Ham-it-up RF up converter. Without this the RTL8192 dongle wouldn't be able to receive below 50MHz however with the onboard crystal on the up-converter, HF is receivable from 125MHz onwards. The up-converter can be enabled by selecting the second from the left switch and doing so automatically incorporates the offset adjustment for the display (or shows that an offset should be applied in the case of the server mode).

Two 5300mAH lithium ion batteries and an on-board charger / boost circuit power the Raspberry Pi for hours.

I plan to incorporate RTTY, AIS and ACARS decoding into future software builds. If there is enough interest I'll release the schematics and source code.

YouTube videos:

Overview

Standalone mode

Server mode