Updating an Aging Global Specialities HP-1 Digital Designer: Part 1–Introduction

HP-1 Digital DesignerThe HP-1 Digital Designer is a device that I bought from E-bay several years ago an until recently it had not received much love from me if I am honest.  If you are not sure what an HP-1 Digital designer is, and I guess there is a fair chance that you wont have encountered one, think super dooper breadboard!  A breadboard, function generator, power supply, logic analyser and more built into one workstation. 

Mine has clearly seen a hard life, now aged, yellowed and partly functioning.  This is the first instalment in its journey back to greatness.  While I doubt many of you will be refurbishing one of these, along the way we should see some of the circuits required to build your own workstation.

Every story has to have a beginning, and for me the first time I became aware of this device was when I was trawling E-bay around four years ago.  Looking for breadboards and I saw the HP-1 and thought that it looked useful.  I bought it for £25 and used it for a little while.  I moved home not long after and the HP-1 kind of made its way to the back of a cupboard.  Recently I dug it out because I wanted use of its function generator and power supply for an experiment in controlling cooling fans.  It was when doing so that I realised that this tool was wasted sitting in a cupboard.

SHP-1 Side Viewpecifications

The HP-1 is a desktop tool that holds at a convenient angle three standard breadboards, a bench power supply, logic indicator LEDs, suited to virtually any type of IC bread-boarding,  Amongst its features are:

  • 3 Solderless Breadboards
  • Fixed 5V DC output
  • 2 DC Outputs - Switch selectable +/- 3.3V, 6V, 9V, 12V, and 15V dc @ 0.5A (all ranges)
  • 6 Clock Frequencies. 1Hz, 10Hz, 100Hz, 1KHz, 10KHz, and 100KHz (tolerance on all ranges ±25%)
  • 8 Logic Switches.
  • 8 Buffered Logic Indicators – Red LEDs (Logic 0 1.5V.)
  • 2 SPDT Logic Switches.
  • Logic Probe.  Switchable to detect either TTL Logic Levels or CMOS Logic Levels.
  • 2 De-bounced Push-button Switches.
  • 2 Uncommitted BNC Connectors.

Logic ProbeYou can see that already it is a useful device, though not useful enough to prevent it’s fall from grace apparently.  I realised pretty quickly the reason that it had not seen the light of day.  You see the HP-1 clearly was designed for prototyping circuits in the days when IC’s (integrated Circuits) such as the 555 timer ruled the roost.  Hobbyists these days are far more likely to be designing circuits based on programmable microcontrollers or development platforms such as the ubiquitous Arduino! 

Using the HP-1 Digital Designer with an Arduino proved to be a pretty difficult proposition,  The slope of the front fascia mean that Arduino just wanted to slide off the front of the designer.  Not only that but as it lost it’s fight to gravity, it kept pulling loose any cables that connected it to my experimental circuit.  I also discovered that the HP-1’s logic probe was damaged and two of the logic indicators were non functioning.  I was pretty convinced that it might be worth more to someone else than me… E-bay?

I thought that if I was going to sell on the HP-1 to it’s hopefully more loving next owner, it would be advantageous to find out a little more about the device.  So began a bit of Google research that surprised me slightly. 

The HP-1 Digital Designer that I own has the brand name Global Specialities on the front.  Apparently the HP-1 has been discontinued by Global Specialties, but I also found it for listed on the website of E & L Products Ltd (formerly known as E & L Instruments Ltd) of Wrexham, North Wales.  I am not sure how much an HP-1 sells for these days, but similar tools are selling for hundreds of dollars!  These tools are generally sold as “trainers” and clearly specialised educational equipment commands a high price.

I am not sure what changed my mind about selling on the HP-1 Digital Designer workstation, but the monetary value of the device perhaps swayed my opinion.  That is not to say that my twenty something year old workstation could fetch that kind of money on an auction site, but perhaps it made me think a little harder about the devices potential.  I started to think that £25 was a bit of a bargain. 

HP-1 Voltage SelectorsRestore or Modify, a Difficult Question?

I briefly thought that it would be a nice idea to simply restore the Digital Designer to as close to new condition that I could.  However this idea was discounted pretty quickly.  I figured that although workstations of this ilk are expensive purchases, this is is more to do with the very limited market that they are sold to than their rarity or popularity.  My HP-1 also is unlikely to be easy to restore to it’s original beauty.  The case is made of that softish plastic that yellows badly over the years and the screen print on the fascia has been scraped away in places.  Take into account that the same model is listed on E & L’s website and it seems pretty daft to spend lots of money and time when a new or nearly new one can no doubt be purchased.

So the next best thing I thought was to look into how I could make the workstation fit my needs.  A plan was born, and a pretty simple one at that. 

  • Clean the HP-1 Digital Designer up as much as can be done easily
  • Fix what is broken (Logic Probe and Logic Indicators)
  • Calibrate the power supplies
  • Add additional features to the device to make it more suited to my needs…


Well not so fast there… In terms of getting the device operational again, I did not see too many issues.  Deciding what additional features would be useful to me.  Well lets just say that I have some ideas, but it is at the this point in time a bit of an open book.

What’s inside a Global Specialities HP-1 Digital Designer?

HP-1 OpenedOpening up the workstation is not a difficult task at all.  On the front panel there are 12 screws, all pozi-drive and all easy to remove.  Once the screws are removed we get a chance to see inside. 

The most abundant component of the workstation is fresh air.  Not that I was expecting the interior to be crammed.  Weighing in at 3.2Kg it is obvious that the wedge shaped bulk of the workstation is there more to create a comfortable slanted surface than it is about holding complex electronics.

The power supply is attached to he plastic base of the unit and comprises of an unmarked transformer and a circuit board which houses bridge rectifiers, capacitors and three TO220 packaged voltage regulators. 

The voltage regulators are:

  • LM317T for the adjustable (-3V to -15V) output
  • LM337T for the adjustable (3V to 15V) output
  • L7805ACV for the 5V and Logic outputs
The L7805 also powers the additional functions of the HP-1 Digital Designer such as the square wave output, logic analyser, pulsers, logic switches and logic indicators.

Front Fascia Flip SideThe rest of the electronics is mounted onto the front fascia panel which it turns out is a large printed circuit board.

The design here gives quite a few clues as to the age of the design.  There are no surface mount components on this board, no microcontrollers either!  Its old fashioned through hole components all the way.  Best of all the integrated circuits that have been used are mounted in sockets as well.  Thinking about the intended use of these workstations in classrooms or on experimenters workbenches, this makes the HP-1 easily serviceable in the case of mishap by a student.

On my example such a mishap has occurred at some time in it’s life with two of the logic indicators not functioning.  My initial thought was that the LEDs had perhaps been overloaded at some point, but the diode tester of my multi-meter told be quickly that this was not the problem.  More on that later…
The integrated circuits used are also common components namely:

  • LM339 Low Power Low Offset Voltage Quad Comparator – used in the logic probes circuit
  • ULN2803A Darlington Transistor Array – used to control the logic indicator LEDs
  • MC74HCT14AN Hex Schmitt-Trigger Inverter – used in the pulsers circuit
  • 74HCT74AN: Dual D-type Flip-flops – Used in the manual push button
  • a second MC74HCT14AN Hex Schmitt-Trigger Inverter – Used in the manual push button and square wave generator circuits
  • KA555 Single Timer – Well, did you expect anything different?  It’s used in the square wave generator to produce the 6 clock frequencies

All of the parts used then are still in production or are available in good supply still.  Of course the later versions of this workstation may have revised circuitry. 

HP-1 Revision InscriptionAs a point of interest, I mentioned earlier that I found the HP-1 had been sold under at least two brand names in it’s history – Global Specialities and E & L Products Ltd. 

Well on the printed circuit board I found the design details for the product and although my workstation is branded Global Specialities, you can see from the inscription that E & L own the Copyright (E & L Instruments is a previous trading name of the company) to at least the PCB design.  I am not sure if my designer dates back to 1986, but the circuit design would appear to be from this year

What Next?

As I complete and write up my work on the HP-1 Digital Designer I will update the site with fresh articles. I will add links here as I complete them.

  • Introduction (Done)
  • Clean-up and Repair (In Progress)
  • Modifying the Power Cable (In Progress)
  • Converting the Breadboard to a Velcro Prototyping area (In Progress)
  • Adding a PIC 16F628 Frequency Counter (In Progress)
  • Upgrading the Clock Signal Generator (Planned)
  • Adding a USB Hub (Planned) and Power source (Planned)
  • Adding Programming Functions for PIC and AVR Processors (Possible)

I am well on my way to updating the Global Specialities Digital Designer to meet more modern requirements but I  have no doubt as time goes on the project will grow in scope.  Once complete i have half an idea that I may build a compact portable version of this tool incorporating any functions that i add to this workstation.