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Wien Bridge Oscillator Design

Wien Bridge Oscillator HPV testing for THD
Wien Bridge Oscillator HPV test­ing for THD

I found myself in need of a very low-dis­tor­tion 1,000 Hz sine wave
gen­er­a­tor for an upcom­ing project.
A quick search on Ebay found sev­er­al used pieces of test equip­ment that met or exceed­ed my require­ments, but were priced at well over $1,000 USD.
I did also find some low-cost China sourced 1 kHz gen­er­a­tor boards, but they had a dis­tor­tion of 0.1% which was way above my 0.005% lim­it.
My cur­rent test gear includes a Keithley 2015 THD Multimeter with a low dis­tor­tion sine wave gen­er­a­tor, but it is only capa­ble of 0.03% THD at 1 kHz.
It was time to see if I could build some­thing for under $100 that would meet my needs.

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Battery Capacity Tester

Battery Tester Assembly Top view
Battery Tester Version 2.2 Assembly top view

I found myself in need of a recharge­able bat­tery tester, so I went off to search the inter­net for a DIY tester.
I was pleas­ant­ly sur­prised to find that John Lowen, had built a Rechargeable Battery Capacity Tester (v2.0), and also devel­oped the PC inter­face soft­ware for desk­top use.
Even bet­ter I found that Paul V. had also built the same tester and had made sev­er­al improve­ment in the design and soft­ware.

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Another ESI 250 DE Universal Impedance Bridge

ESI 250 DE unit #2
ESI 250 DE unit #2 front pan­el

Everyone should have at least two of these ESI 250DE Impedance bridges.

Well that was not my first thought when pur­chas­ing this unit on Ebay.
I was still hav­ing some issues with the “Internal DC” detec­tor cir­cuit on my exist­ing unit, and the price of this unit was extreme­ly rea­son­able. After dozens of hours trou­bleshoot­ing the first unit with no solu­tion, my thought was to com­pare the two cir­cuits and sal­vage parts from the new unit if nec­es­sary.

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Mettler K4T Balance

Cleanup and check of a Mettler Instruments K4T sin­gle pan top load­ing bal­ance.

Mettler K4 balance front left view
Mettler K4 bal­ance front left view

After own­ing and using this K4T bal­ance for over twelve years, I thought it was time for a full cleanup and accu­ra­cy check. When first pur­chased from Ebay it received a quick cleanup, func­tion, and accu­ra­cy check, before I quick­ly put it to use.

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