The High Nibble

# Step-by-step Assembly Guide (Draft)

# Notices

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Please read all the following notices and instructions before assembling the IMSAI 8080esp replica kit.

WARNING

This kit contains cut acrylic. Cut acrylic can have sharp edges that can in turn cut. As a precaution, wear cotton gloves to protect your hands while handling the cut acrylic.

CAUTION

This kit contains many small parts that may be a choking hazard and is not suitable for children. Keep the contents of this kit away from children to avoid choking.

NOTE

This kit is for hobby and educational interest only. The simulated replica computer you will build should not be used for any other purpose and cannot be expected to work reliably beyond a demonstration of the simulated computer.

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Keep the box the IMSAI 8080esp replica kit shipped in. This custom made box was designed to both ship the unassembled kit and also to house the assembled replica. It is the best box you can use if you need to store or transport your finished IMSAI 8080esp.

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Keep one of the full sheets of cardboard from above or below the components. This will serve as a tool to help with the assembly of the kit, especially for retaining the M4 bolts in the correct position while assembling all the layers of acrylic and the PCB together. It maybe useful to you in future if you ever need to disassemble and reassemble the IMSAI 8080esp.

Notes on the PCB

  • There is no resistor R15, it was removed from the design long ago and the resistors were never renumbered
  • There are 2 silk screen errors on the PCB (v3.4.1, fixed on v3.4.2):
    1. the LED LA14 is incorrectly labeled as LS14
    2. the LED LD0 is labeled on the left of the LED and should be labeled above as per LD1-LD7
  • There is a 5x2 group of through-holes marked Spare that nothing gets soldered into
  • There are two groups of 8x1 through-holes that are unmarked (one above LRN1 and one below RN1) that nothing gets soldered into

Note

This step-by-step assembly guide refers to the front and back of the PCB as follows:

  • the front of the PCB has the silkscreen for the LEDs and the toggle switches
  • the back of the PCB has the silkscreen of the IMSAI 8080 Microcomputer System decal and The High Nibble logo

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There is a play list of videos on YouTube that demonstrate this step-by-step assembly sequence and includes additional tips for successful assembly.

# Unpacking and checking against the BOM

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Please unpack the entire kit and perform a stock take of what you have received against the Bill-of-Materials.

WARNING

If you believe you are missing any components when you compare the kit contents with the Bill-of-Materials please contact me directly by email to info@thehighnibble.com.

Please respect that this kit is a hobby project made by an individual maker and not a mass produced product from a manufacturer. While every care was taken to pack each kit correctly, mistakes may have occurred.

DAMAGE

If your kit arrived in a damaged state, or if upon opening the kit you find any of the contents to be damaged, please take photographs of the damage and include them in your email.

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I will happily work with you directly, via email, to resolve the issues with your incomplete or damaged kit. This may require mailing replacement parts to you and that will take time, so please have patience.

# PCB & Soldering

# ESP32 Microcontroller, PSRAM & micro SD Card Socket

Step Parts Location Notes
1. Header 20x1 Male ESP32-PICO-KIT board Before soldering anything to the main circuit board, it's first necessary to solder some pins to the ESP32-PICO-KIT board. Cut 2 sets of 3 pins from the 20x1 Male Header strip. Solder these into the unpopulated through-holes on the ESP32-PICO-KIT board. Upon completion there should be 20 pins along each edge of the underside of the ESP32-PICO-KIT board.
2. PSRAM (SMD) U13 front Note: Pin 1 is indicated on the PCB by a white dot and on the component by a dimple in the plastic case. When done, perform a continuity test with a multimeter from each pin of the SOP-8 package to a connected pad on the PCB (see video, details to follow)
3. microSD Card Socket (SMD) uSD Card front The microSD Card Socket is also soldered to the front of the circuit board. Align the two locating pins on the microSD Card Socket with the two holes in the PCB. Solder the 4 large ground pads of the lid first ensuring the 9 smaller leads are well aligned, then solder the 9 smaller leads.
4. Resistor 10K Ohm R14 front There are 15 10K resistors in this kit (including 1 spare), and they are colour-coded Brown, Black, Orange, Gold. The resistors are tight fitting, so bend the leads close to the their body before inserting into location. Resistors are not polarized, and can be soldered in either orientation.
5. Capacitor 100nF C1 front There is only one type of capacitor in this kit, and they can be soldered in either orientation.
6. Resistor Network 6x10K Ohm RN1 back Note: Pin 1 is indicated on the PCB by the square pad and on the component by a white dot
7. Connector 20x1 Female (x2) ESP32 back Solder these connectors mounted on the back of the PCB in the 2 rows of 20 through-holes that form a DIP40 outline marked ESP32.
8. ESP32-PICO-KIT, microSD Memory Card [TEST STEP] Plug the ESP32-PICO-KIT into the female connectors on the back of the PCB. Note: The USB connecter should be towards the near edge of the PCB and the Wi-Fi antenna towards the RS232 connector mounting holes. Insert the microSD card. Connect the ESP32-PICO-KIT to a PC with a suitable USB cable. Run a terminal emulator (e.g. PuTTY on Windows, or iTerm2, Serial on Mac) at 115200 baud 8N1 connected to the TTY/COM port that the ESP32-PICO-KIT presents and observe the boot logs. Errors with either the PSRAM or the microSD card will indicate soldering mistakes (see the During Assembly section in the Troubleshooting guide for details)

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If you do not see a TTY/COM port on your PC presented by the ESP32-PICO-KIT, you may need to install a driver for the Silicon Labs CP210x USB to UART bridge used on the ESP32-PICO-KIT. See Serial Communications (RS232, USB) in the Configuration guide for details.

WARNING

Before continuing, remove both the microSD Memory Card from the socket and the ESP32-PICO-KIT from the female connectors, taking care not to bend the Wi-Fi antenna.

# LEDs and accompanying Resistors

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The LEDs and accompanying Resistors should be soldered in groups of 8 as indicated below and each group of 8 tested before proceeding to the next group.

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Use the supplied acrylic spacer and alignment tools. Tape them in place with the LEDs before you solder to help achieve the alignment of each group of 8 LEDs.

  • My preference is to raise the LEDs 3mm off the PCB, the acrylic spacer with 8 open vertical slots enables this. You can, however, solder the LEDs sitting flush with the PCB.
  • The acrylic alignment tool with 8 round holes should always be used to help align 8 LEDs at a time to be in alignment. Peel any covering off the alignment tool before using it.

(see video, details to follow)

WARNING

LEDs are polarized and must be soldered in the correct orientation. The cathode (short lead, nearest the flat edge) should be soldered in the square, lower, though-hole pad. The anode (long lead) should be soldered in the round, upper, though-hole pad. Check the orientation of all LEDs in each group of 8 before soldering into place by visually inspecting the flat edge corresponding with the flat indicated in the silk screen on front side of the PCB, and the alignment of the long and short leads on the back side of the PCB.

Step Parts Location Notes
9a. LED Red 5mm (x8) LA8-LA15 front Note: LEDs are polarized and must be soldered in the correct orientation. Use the acrylic spacer and alignment tools. See notes above.
10a. Resistor 3K Ohm (x8) R32-R39 front There are 45 3K resistors in this kit (including 1 spare), and they are colour-coded Orange, Black, Red, Gold. Resistors are not polarized and can be inserted and soldered either way around. Because of my sense of aesthetic (ok, my OCD) I like to orientate them all the same way according to the coloured bands.
11a. Test Lead [TEST STEP] At this time you should test the group of 8 LEDs you have just soldered into place. Insert the ESP32-PICO-KIT into its socket and connect it to a power source. Using the supplied test lead you can use the +5V provided by the ESP32-PICO-KIT to the PCB to test each LED (see video, details to follow)

WARNING

Before continuing, remove both the microSD Memory Card from the socket and the ESP32-PICO-KIT from the female connectors, taking care not to bend the Wi-Fi antenna.

# Steps 9-10 can now be repeated for each remaining group of LEDs in the following suggested order

Step Parts Location Notes
9b. LED Red 5mm (x8) LS0-LS7 front
10b. Resistor 3K Ohm (x8) R40-R47 front Orange, Black, Red, Gold
11b. Test Lead [TEST STEP]
9c. LED Red 5mm (x8) LO0-LO7 front
10c. Resistor 3K Ohm (x8) R16-R23 front Orange, Black, Red, Gold
11c. Test Lead [TEST STEP]
9d. LED Red 5mm (x8) LA0-LA7 front
10d. Resistor 3K Ohm (x8) R24-R31 front Orange, Black, Red, Gold
11d. Test Lead [TEST STEP]
9e. LED Red 5mm (x8) LD0-LD7 front
10e. Resistor 3K Ohm (x8) R52-R59 front Orange, Black, Red, Gold
11e. Test Lead [TEST STEP]
9f. LED Red 5mm (x4) LHT1, LWT1, LRN1, LIE1 front
10f. Resistor 3K Ohm (x4) R48-R51 front Orange, Black, Red, Gold
11f. Test Lead [TEST STEP]

# Other Resistors, Capacitors, IC sockets & Miscellaneous Parts

Note

The transistor Q1 and the accompanying Resistor R13 are optional. They are a convenience for flashing new firmware on the ESP32-PICO-KIT over USB without removing it from the IMSAI 8080esp PCB. However, on their own they do not provide the whole solution and two extra jumper wires are required to be directly soldered to component leads on the ESP32-PICO-KIT board (details to follow). The simple alternative is to remove the ESP32-PICO-KIT from the IMSAI 8080esp PCB before flashing new firmware over USB, or more simply use the drag-and-drop, over-the-air (OTA) firmware update procedure via the Desktop UI (details to follow).

Step Parts Location Notes
12. Resistor 10K Ohm R1-R12 front Brown, Black, Orange, Gold. Resistors are not polarized and can be inserted & soldered either way around. Because of my sense of aesthetic (ok, my OCD) I like to orientate them all the same way according to the coloured bands.
13. Resistor 10K Ohm R13 back (Optional) See note above. Brown, Black, Orange, Gold.
14. Capacitor 100nF (0.1μF, 104) C3-C12, C17 front These capacitors are not polarized and can be inserted & soldered either way around.
15. Capacitor 100nF (0.1μF, 104) C2, C13-C16 back These capacitors are not polarized and can be inserted & soldered either way around.
16. 16 pin DIP Socket (x10) U1-U10 front DIP sockets should be inserted to align the crescent/indent at one end with the corresponding mark in the silk screen for the IC Socket. This makes no difference functionally, but will help with the inserting the ICs with the correct orientation later in the assembly.
17. 16 pin DIP Socket U11 back DIP sockets should be inserted to align the crescent/indent at one end with the corresponding mark in the silk screen for the IC Socket. This makes no difference functionally, but will help when inserting the ICs with the correct orientation later in the assembly.
18. S8050 NPN Transistor Q1 back (Optional) See note above.
19. Tactile Switch SPST-NO Reset front Note: don't rely only on the 2 soldered connector pins to secure the switch to the PCB, also solder in the 2 mounting pegs to ensure a secure connection to the PCB
20. Header 4x2 Male Boot back
21. Header 8x2 Male Patch back
22. Header 8x2 Male Comms back
23. DE9 (DB9) Male Socket (x2) RS232-1, RS232-2 back Note: don't rely only on the 9 soldered connector pins to secure a socket to the PCB, also solder in the 2 mounting pegs to ensure a secure connection to the PCB

# Inserting the ICs

WARNING

If you fail to insert the ICs at this step, before proceeding to insert and solder the rocker/toggle switches, you will find that you cannot later insert some of the ICs without bending the switches. I have done this, to prove that it can be done, but I do not recommend it.

WARNING

ICs are polarized/directional and must be inserted in the correct orientation. ICs should be inserted to align the crescent/indent at one end with the corresponding mark in the silk screen. If you have soldered in the 16 pin DIP Sockets with the indicated orientation, this will make the job easier. Once you have inserted the ICs, have a cup of tea and then double-check they are in the correct way: it's easy to accidentally insert them the wrong way round.

Step Parts Location Notes
24. 74HC595 (x6) U1-U6 front U1-U6 are all oriented the same way, with the crescent/indent to the right when looking at the front of the PCB. Take time to check you are putting the ICs in the correct sockets, as U6 might not be where you expect it to be.
25. 74HC165 (x4) U7-U10 front U7-U10 are all oriented the same way, with the crescent/indent to the right when looking at the front of the PCB.
26. MAX3232 U11 back U11 is oriented with the crescent/indent to the left when looking at the back of the PCB.

# Testing I

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At this point you can operate the IMSAI 8080esp without having the rocker/toggle switches mounted.

  • Plug the ESP32-PICO-KIT into the female connectors on the back of the PCB.
  • Note: The USB connecter should be towards the near edge of the PCB and the Wi-Fi antenna towards the RS232 connectors.
  • Insert the microSD card.
  • Connect the ESP32-PICO-KIT to a USB power source with a suitable USB cable.
  • The simulation will not start until you short the centre and top pins of switch S1

You can connect to the web based desktop UI by connecting a PC to the Wi-Fi SSID advertised as IMSAI8080. Because the Wi-Fi has not been configured, the IMSAI 8080esp should have rebooted into Wi-Fi fallback mode, where it acts as an Access-Point (AP) with the default SSID of IMSAI8080. Once you are connected to this Wi-Fi network, start a Chrome browser and enter the URL http://imsai8080.local.

There are (or will be) separate instructions for configuring the Wi-Fi to connect to you local Wi-Fi network.

You can use the virtual CPA: device to toggle the RUN/STOP switch.

WARNING

While you can operate the IMSAI 8080esp at this point, it will not do much for you without some further configuration. The default configuration is like an empty machine with no ROM only RAM, and you don't have a full front panel to play with. Damn! Configuration is (or will be) covered elsewhere.

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Time for a cup of tea if you've gotten this far.

# Rocker/Toggle Switches

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To correctly locate and align the rocker switches before soldering, the front panel should be partially assembled according to the following instructions.

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Many of the sheets of acrylic have a protective backing cover (plastic or paper) to protect them from scratching during cutting and transportation. This should be removed before you use them in the assembly of the kit.

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When assembling all or part of the front panel it is sometimes necessary to flip the assembly. To avoid having the M4 socket screws fall out you can use masking tape to hold them in place, or use a cardboard sheet from the packaging to cover the socket screws while flipping the assembly (see video).

WARNING

When screwing the M4 Nylon Nuts and the M4 Socket Screws together only ever make them finger tight to avoid stripping the thread from the M4 Nylon Nuts.

Step Parts Location Notes
27. M4x30mm Hex Socket Screw (x8) 3mm Black acrylic LED/switch masking plate Insert the 8 M4 socket screws into each of the 8 round holes in the large 3mm Black acrylic LED/switch masking plate
28. Spacer 8mm Nylon (x8) Thread a 8mm spacer over each of the 8 M4 socket screws behind the 3mm Black acrylic LED/switch masking plate
29. PCB Fit the PCB over the 8 M4 socket screws behind the 8mm spacers and the 3mm Black acrylic LED/switch masking plate
30. M4 Hex Nut Nylon (x8) Secure this partial assembly of the front panel by screwing a M4 Nut on each of the 8 M4 socket screws behind the PCB

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You should now have a sandwich with the PCB at the back and the 3mm Black acrylic LED/switch masking plate at the front, separated by the 8mm spacers and held together with the M4 socket screws and nuts.

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As you insert each rocker switch into the PCB, there should be a slight press-to-fit resistance from the pins as they push into the through-holes in the PCB. This will help hold the switch in position prior to soldering.

Step Parts Location Notes
31a. Blue Rocker (On-On) (x4) SA12-SA15 Don't solder them yet
32a. Red Rocker (On-On) (x4) SA8-SA11 Don't solder them yet
33a. 3mm Black acrylic LED spacer & switch alignment guide (8 slots) SA8-SA15 Place the small acrylic alignment guide over the ends of the whole set of 8 rocker switch toggles/actuators, this should help get the switches in alignment. Secure this in place with tape of a couple of strong elastic bands. Solder the switches in place.

# Steps 31-33 can now be repeated for the second group of (On-On) switches

Step Parts Location Notes
31b. Blue Rocker (On-On) (x4) SA4-SA7
32b. Red Rocker (On-On) (x4) SA0-SA3
33b. 3mm Black acrylic LED spacer & switch alignment guide (8 slots) SA0-SA7

WARNING

The order of the momentary switches is different. They alternate blue/red from left to right with the red power switch in the right-most position. I have seen different configurations and I guess it comes down to personal choice. I imagine you can swap the plastic toggle actuators but I have not tried this myself.

Step Parts Location Notes
34. Blue Rocker (Mom-off-Mom) (x3) S6, S4, S2 Don't solder them yet
35. Red Rocker (Mom-off-Mom) (x2) S5, S3 Don't solder them yet
36. 3mm Black acrylic LED spacer & switch alignment guide (8 slots) S2-S6 Place the small acrylic alignment guide over the ends of the whole set of 5 rocker switch toggles/actuators, this should help get the switches in alignment. Secure this in place with tape of a couple of strong elastic bands. Solder the switches in place.
37. Red Power Switch (On-On) S1 Solder it in place.

# Testing II

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At this point the IMSAI 8080esp should be fully operational. See Testing I for a general outline of getting it started.

You should exercise all the switches and make sure they are operating correctly (details to follow)

WARNING

While you can operate the IMSAI 8080esp at this point, it will not boot a disk without further configuration. The default configuration is like an empty machine with no ROM only RAM. You can, however, now enter programs through the front panel switches and run them.

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Time for another cup of tea if you've gotten this far.

# Full Front Panel Stack

WARNING

Having successfully gotten this far, the next section can go very smoothly if you take care or it can become very fiddly and frustrating if you rush or end up separating the PCB and the 3mm Black acrylic LED/switch masking plate

TIP

  1. Remove the M4 Nuts (8) without letting the M4 Socket Screws (8) drop out of place, tape may help.
  2. Place the PCB down on a surface with the 3mm Black acrylic LED/switch masking plate facing up, the M4 Socket Screws will need to slide up to let the PCB sit down flat on the surface.
  3. Carefully remove the M4 Socket Screws (8) without disturbing the 3mm Black acrylic LED/switch masking plate, the PCB and especially don't allow the 8mm Spacers to move out of place.
  4. Leave this assembly undisturbed while you put the remaining front panel acrylic together
Step Parts Location Notes
38. M4x30mm Hex Socket Screw (x8) 6mm Clear acrylic front cover Insert the 8 M4 socket screws into each of the 8 round holes in the thick 6mm Clear acrylic front cover. Tape over the heads to hold them in place.
39. 3mm White text/decals on Black facia over red transparent filter Align the Text Facia over the M4 socket screws and slide it down to meet the clear acrylic
40. This step removed as the Text Facia and transparent red filter are now a single piece

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  1. Take this whole assembly and flip it over, with the clear acrylic and the Text Facia facing up.
  2. Lower this into place, guiding the M4 socket screws through the holes in the other assembly you previously set aside (black acrylic, 8mm spacers and PCB)
  3. Making sure the M4 socket screws wont fall out (tape again), flip this whole assembly over, placing the front panel face down on a surface.

WARNING

If by this point, any of the 8mm Spacers have slipped out of position, you can withdraw the corresponding M4 socket screw and use tweezers to correctly locate the 8mm Spacer before reinserting the M4 socket screw

Step Parts Location Notes
41. Spacer 6mm Nylon (x8) Thread a 6mm spacer over each of the 8 M4 socket screws behind the PCB
42. 3mm Clear acrylic back cover Align the 3mm Clear acrylic back cover over the M4 socket screws and slide it down to meet the 3mm Spacers
43. M4 Hex Nut Nylon (x8) Push a M4 Nut into each hexagonal cutout in the 3mm Clear acrylic back cover behind each of the 8 M4 socket screws, tape them into position so that they don't fall out while tightening the M4 socket screws

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  1. Holding the whole assembly firmly together (again tape may help) stand it up on one long edge.
  2. Screw each of the 8 M4 socket screws firmly into their corresponding M4 Nut, take care not to over-tighten and strip the thread in the M4 Nut.

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Almost done!

Who would have thought you'd have a working replica of an IMSAI 8080 in around just 40 simple steps 😃

Probably time for another cup of tea, but in my case, I think I'd choose something stronger.

# Switch Surround

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Don't try to operate your IMSAI 8080esp for long periods of time without this component in place. It looks so good, you're missing out if you don't have it in place 😃.

WARNING

Don't attach any tape to the 6mm Charcoal grey hammer tone painted acrylic switch surround There has been a report of this removing some paint when the tape was removed.

Step Parts Location Notes
44. 120mm x 25mm Black Velcro adhesive backed hook & loop tape Cut both the hook and loop tape into 2 x 60mm lengths. Cut each 60mm piece lengthways in half to produce 4 x 60mm x 12.5mm strips of hook and loop tape
45. 60mm x 12.5mm Black Velcro adhesive backed hook & loop tape (x4) 6mm Charcoal grey hammer tone painted acrylic switch surround Stick each strip of hook and loop tape to the back of the switch surround vertically , aligned behind the fingers extending upwards along the switch surround
46. 6mm Charcoal grey hammer tone painted acrylic switch surround Remove the paper backing from the hook and loop tape and press the switch surround into place under the toggle switches on the assembly you completed after Step 43.

# The Lid

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The lid can wait, its time to play!

WARNING

It is highly recommended that you fit the 2mm White acrylic back cover corner reinforcement pieces to the 3mm Clear acrylic back cover before you you attach the lid. Failure to do so might result in cracking the 3mm Clear acrylic back cover.

Step Parts Location Notes
47a. 2mm White acrylic back cover corner reinforcer (x3+1) (top edge crucifix slots) 3mm Clear acrylic back cover See this forum post for details.
47b. 2mm White acrylic back cover corner reinforcer (x4) (bottom side edge crucifix slots) 3mm Clear acrylic back cover See this forum post for details.
48. M3x12mm Black Machine Screw (x4), M3 Nut (x4) 3mm Blue aluminium lid Put an M3 Screw through each of the 4 smaller holes in the Blue aluminium lid and use a M3 Nut on the end of each M3 Screw to secure the Blue aluminium lid.
49. 3mm Blue aluminium lid Place the Blue aluminium lid around the assembly completed at step 38 above. The M3 Screws are closer to the back than to the front. Secure each M3 Screw & M3 Nut in the corresponding slot in the 3mm Clear acrylic back cover. Don't over-tighten the M3 Screws used to secure the lid or you could crack the 3mm Clear acrylic back cover.

# Celebrating

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Once that last "cup-of-tea" has had the desired calming effect...

The most appropriate way to celebrate is to toggle in and run your first program.

  1. Remember to once again plug in the ESP32-PICO-KIT and insert the microSD Card
  2. Connect the ESP32-PICO-KIT to a USB power source with a USB micro-B cable
  3. Go and download/open your copy of the IMSAI 8080 Microcomputer System User Manual (also included in the manual folder on the microSD card)
  4. Find page 34 in the manual and start from the heading SYSTEM FUNCTIONAL TEST

Enjoy!

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To do anything more than toggle programs into a machine with no stored programs in ROM, you will need to understand how to Configure your IMSAI 8080esp to load ROM images on startup, connect to Wi-Fi to access the Desktop UI, etc...

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Last Updated: 10/5/2022, 4:16:56 AM