Old Micronta (Radio Shack / Tandy) Digital Multimeter with retro LED display - Page 1
Forum section: electronics / testgear

author: Fryode
author_rank: Newbie
timestamp: March 06, 2018, 02:34:43 pm
content: Hello, all.I've been lurking for a while now, but I found something I thought would be worth sharing as my first post.At a local thrift shop, I found an old DMM that caught my eye as unique, as I had never seen one with the calculator-style 7-segment magnified LED numbers.The leads are regular banana jacks, just not shielded.I was a bit surprised to see a green Radio Shack 9-volt battery inside. Those were gone a long time ago.I can't see a model number anywhere. Has anyone else seen one of these before?I snapped a photo, but the digits don't show up, dim as they are.

author: Brumby
author_rank: Unknown
timestamp: March 06, 2018, 02:36:28 pm
content: The battery - yes ...... the meter - no.

author: glarsson
author_rank: Frequent Contributor
timestamp: March 06, 2018, 02:46:27 pm
content: Search for "Sinclair PDM 35 multimeter" for the original.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 06, 2018, 02:47:13 pm
content: Back in those days, LEDs were both very dim and very power hungry.Additionally, they were multiplexed.Calculator manufacturers used tiny lenses in an effort to make the display more visible.It is obvious from the picture that, in an effort to reduce development and tooling costs, borrowed many components from a common calculator.Have you checked its calibration, comparing it against a known good multimeter?? I would be very curious.

author: Fryode
author_rank: Newbie
timestamp: March 06, 2018, 02:56:28 pm
content: Wow! I knew it had to be someone else's design (a la the TRS-80 Model 100). Thank you and well played.Sinclair, though. The same store I bought it from used to have an insane amount of Clive's computers back in the late 1980s. I never had one, regrettably.

author: Fryode
author_rank: Newbie
timestamp: March 06, 2018, 03:04:36 pm
content: It's as far off as it says on the tape above the display. Well, technically (loathing shudder ensues*), it's 4.83V when compared to a source that's calibrated to 4 digits right of the dot.* "Technically" is, unfortunately, mostly used by people who are trying to win a debate, not educate.

author: Kean
author_rank: Unknown
timestamp: March 06, 2018, 04:00:07 pm
content: I remember those - they somewhat resembled an early HP calculator - except in build quality. A post showing the Sinclair version:https://www.eevblog.com/forum/reviews/sinclair-pdm-35-dmm/Thankfully my first mutimeter was a Micronta LCD model from Tandy (Radio Shack) Australia - early 80's I'd guess. I still have it around somewhere, the digits were pretty small as I recall. And I've never seen another one like it, so it can't have been a popular model.

author: Fryode
author_rank: Newbie
timestamp: March 06, 2018, 04:26:06 pm
content: My first meter was an analog galvo needle thing my Grandpa gave me. The probes weren't standard, but it fit in my pocket and worked well enough. I lost the back cover over the years, but I still have the meter in a box somewhere.Then again, I'm also almost 40 and Grandpa gave me that meter when I was 7.Grandpa also gave me my first DMM. I still have it less than a meter away, actually... Radio Shack 22-181. I blew out the DC high-current modes over 20 years ago and blew out continuity a week ago. My Fluke 123 has taken over until I can grab a replacement for the aforementioned meter. Based on the Radio Shack date code sticker of 9A3, it was made in September 1993 so it's close to 25 years old.